China has suffered some of the effects of global warming, and one of the
potential implications of climate warming is the alteration of the
temporal–spatial patterns of water resources. Based on the
long-term (1960–2008) water budget data and climate projections from
28 global climate models (GCMs) of the Coupled Model Intercomparison Project
Phase 5 (CMIP5), this study investigated the responses of runoff (R) to
historical and future climate variability in China at both grid and catchment
scales using the Budyko-based elasticity method. Results show that there is a
large spatial variation in precipitation (P) elasticity (from 1.1 to 3.2)
and potential evaporation (PET) elasticity (from -2.2 to -0.1) across
China. The P elasticity is larger in north-eastern and western China than in
southern China, while the opposite occurs for PET elasticity. The catchment
properties' elasticity of R appears to have a strong non-linear relationship
with the mean annual aridity index and tends to be more significant in more
arid regions. For the period 1960–2008, the climate contribution to R
ranges from -2.4 to 3.6 % yr-1 across China, with the negative
contribution in north-eastern China and the positive contribution in western
China and some parts of the south-west. The results of climate projections
indicate that although there is large uncertainty involved in the 28 GCMs,
most project a consistent change in P (or PET) in China at the annual
scale. For the period 2071–2100, the mean annual P is projected to
increase in most parts of China, especially the western regions, while the
mean annual PET is projected to increase in all of China, particularly the
southern regions. Furthermore, greater increases are projected for higher
emission scenarios. Overall, due to climate change, the arid regions and
humid regions of China are projected to become wetter and drier in the
period 2071–2100, respectively (relative to the baseline 1971–2000).
Introduction
Climate change has become increasingly significant (IPCC, 2013), and numerous
studies have reported that climate warming is likely leading to the
alteration of the hydrological cycle (Oki and Kanae, 2006; Jung et al.,
2010). The dynamic properties of the hydrological cycle are governed by the
interactions and feedbacks between atmospheric and land surface hydrologic
processes on a catchment scale. The potential consequences of anthropogenic
climate change on the hydrological cycle have received significant attention
over the last 2 decades (Wang et al., 2012; IPCC, 2013).
Runoff (R), as a commonly adopted indicator of the hydrologic cycle, is
critical to human lives and economic activities (Milly et al., 2005). There
is a great deal of previous work exploring the impact of climate variations
on R, with the motivation stemming from the region's vast resources
(Christensen et al., 2004; Guo et al., 2009; Piao et al., 2010; Chen et al.,
2012; Harding et al., 2012; Wang et al., 2012; Y. P. Xu et al., 2013), dangers of
flooding (Kay et al., 2006, 2009, Kay and Jones, 2012; Raff et al., 2009; Liu et al., 2013;
Xiao et al., 2013; Wang et al., 2013; Smith et al., 2014; Wu et al., 2014,
2015), and agricultural water uses (Vano et al., 2010). The most common
practices in these previous studies are to use the hydrological models
driven by the output from global climate models (GCMs) to simulate the
hydrological process (e.g. R) under future climate change scenarios.
However, the key issue faced by such studies is the need to convert coarse-resolution GCM outputs to local catchment-scale climatic variables at a
higher spatial resolution to serve as the input to a hydrological model
(Vano et al., 2015; Wu et al., 2015). The impact assessments are resource-intensive and usually subject to uncertainties related to the choice of
hydrological model, GCMs, emissions scenarios, and downscaling techniques
(Vano et al., 2014, 2015).
With the uncertainty in R due to climate change, simple tools able to provide
robust estimates of this impact are essential to support policy and planning
decisions. Climate elasticity, as an important indicator, provides a measure
of sensitivity of the changes in R due to the changes in climate. Schaake (1990)
made the first attempt to introduce the concept of elasticity and
related the climate elasticity of R to precipitation (P). Since then numerous
climate elasticity methods have been developed for evaluating the hydrologic
response to climate change all over the world (Schaake, 1990; Dooge et al.,
1999; Sankarasubramanian et al., 2001; Milly and Dunne, 2002; Fu et al.,
2007; Zheng et al., 2009; Ma et al., 2010; Yang and Yang, 2011; Yang et al.,
2014; Vano et al., 2015). Sankarasubramanian et al. (2001) provided a
detailed category of climate elasticity methods for modelling climate change
impacts. One of the most common methods is to analytically derive the
sensitivity of R based on the Budyko hypothesis, due to its clear theory
and the fact that it does not rely on a large amount of data (Yang and Yang, 2011). More
importantly, the Budyko-based elasticity method can derive the climate
elasticity and can also represent the impact of the catchment
characteristics through the parameters of the Budyko model. Accordingly, it
is widely applied for the assessment of the hydrologic impacts of climate
change (Dooge et al., 1999; Zheng et al., 2009; Yang and Yang, 2011; Yang et al., 2014).
China is a vast land, spanning many degrees of latitude with complicated
terrain, which results in a large regional variation in climate elasticity.
The investigation of the P elasticity of R has been reported in many regions
of China, such as the Miyun Reservoir basin (Ma et al., 2010), Luan River
basin (X. Y. Xu et al., 2013), the headwater catchments of the Yellow River basin
(Zheng et al., 2009), Poyang Lake basin (Sun et al., 2013), and Hai River
and Yellow River basins (Yang and Yang, 2011; Liu and McVicar, 2012).
Recently Yang et al. (2014) investigated the climate elasticity of R for the
210 catchments of China based on the Budyko-based elasticity approach. The
results indicated that the P elasticity exhibits a large regional variation,
with a small range in southern China, the Songhua River basin, and the
north-west and a large range in the Hai River basin, the Yellow River basin,
and the Liao River basin. Although the aforementioned studies have certainly
made advances in understanding the climate elasticity of R in China, our
knowledge about the responses of R to climate change over various temporal
and spatial scales remains rather limited due to the large regional
variation in climate types and catchment characteristics. The question of
how climate change will affect R over China in the future is also an
important problem to be addressed. Developing a more accurate and
quantitative understanding of the changing water resources over various
temporal and spatial scales under a changing environment is therefore a high
priority for China.
Based on the unique long-term (1960–2008) land surface dataset of China and
the climate projections from 28 GCMs of the Coupled Model Intercomparison
Project Phase 5 (CMIP5), the objectives of this research are (1) to
investigate the changes of R and climate variables and their relationship at
an interannual scale; (2) to quantitatively estimate the climate elasticity
and catchment properties' elasticity of R across China at both grid and
catchment scales; and (3) to predict climate change and the changes in R due
to future climate change for China from the CMIP5 projections at both grid
and catchment scales.
Location of the main river basins in China. The numbers denote the
river basins with increasing aridity index: (1) Southeast Drainage (0.52);
(2) Pearl River (0.64); (3) Yangtze River (0.81); (4) Southwest Drainage (1.19);
(5) Huaihe River (1.19); (6) Heilongjiang River (1.43); (7) Liaohe River (1.71);
(8) Haihe River (2.14); (9) Yellow River (2.38); (10) Inner Mongolia River (4.41);
(11) Qiangtang River (4.70); (12) Qinghai River (6.68); (13) Xinjiang River (8.09),
(14) Hexi River (8.63). The numbers in the parentheses indicate the
1960–2008 mean aridity index.
Data and methodologyDatasets
Monthly data of potential evaporation (PET) covering the period 1960–2008 over
China are provided by the Terrestrial Hydrology Research Group of Princeton University
(Sheffield et al., 2006, 2012). The PET is estimated by the Penman equation
(Penman, 1948; Shuttleworth, 1993), using the updated meteorological dataset
obtained from Sheffield et al. (2006, 2012). A long-term (1960–2008) daily
land surface dataset over China, including P, surface runoff (RS), and
baseflow (BS), with a 0.25∘ spatial resolution, was obtained from
the Land Surface Processes and Global Change Research Group (Zhang et al.,
2014). In this dataset, P is driven by interpolating gauged daily
precipitation from 756 meteorological stations of the Chinese Meteorological
Administration (CMA). RS and BS are derived from the Variable Infiltration
Capacity (VIC) model forced by the gridded daily climate forcings (i.e. P,
maximum and minimum temperature, and wind speed). VIC model parameters,
including the infiltration shape parameter, the second and third soil layer
depths, and the three parameters in the base flow scheme, were estimated by
using an optimization algorithm of the multi-objective complex evolution of
the University of Arizona (Zhang et al., 2014). The simulated monthly RS and BS
match well with the observations at the large river basins in China (Zhang
et al., 2014). Compared with the global product of a similar nature, this
dataset provides a more reliable estimate of land surface variables over
China (Nijssen et al., 2001; Adam et al., 2006; Rodell et al., 2004; Sheffield
et al., 2006; Sheffield and Wood, 2007; Pan et al., 2012). In this study, the
data of P, RS, and BS are initially regridded onto 0.5∘ grids over China
using the linear interpolation method. All the daily data (P, RS, and BS) and
monthly data (PET) are then aggregated temporally for the annual scale over
China. The R was calculated by the sum of RS and BS for each of the 0.5∘ grid points.
Climate projections from 28 CMIP5 GCMs (as shown in Table 1) are provided by
the Canadian Climate Data and Scenarios (CCDS, http://climate-scenarios.canada.ca/?page=main).
These data, including simulations of surface air temperature (T), P, sea ice
thickness, sea ice concentration, snow depth, and near-surface wind speed,
are statistically downscaled and regridded onto a common 1∘× 1∘
global grid by the CCDS. In this study, monthly P and monthly T over
China, including one historical simulation for the period 1971–2000 and
three emission scenarios (RCP2.6, RCP4.5, and RCP8.5) for the future
period 2071–2100 from each of the 28 CMIP5 models and the multi-model ensemble of
28 CMIP5 models, are used for the projections of climate change. The data
are initially disaggregated to 0.5∘ grids over China then corrected by
using a “delta change” method (Wu and Huang, 2016), on the basis of the
observed data of P and T as provided by the Climatic Research Unit (CRU) of
the University of East Anglia (Harris et al., 2014).
Figure 2 shows the comparison of observed mean annual T and P and the
corresponding simulations from 28 CMIP5 models before and after bias
correction for the 14 basins in China. The basin number is consistent with
that given in Fig. 1. As shown, the uncorrected model simulations tend to
underestimate T and overestimate P for most of the basins, with more
uncertainties for the simulation of P than for T. Compared to the uncorrected
model results, the bias correction results represent large improvements and
show a good agreement with the observed values for these basins. Therefore,
the bias correction model simulations are acceptable for the investigation
of climate change projections in this study.
As the GCM data used only consist of P and T, the PET of GCM is estimated by the
Thornthwaite method (Thornthwaite, 1948) and then corrected by a
multiplicative bias correction method as follows:
PETcor,GCM,i=PETTh,GCM,i×PET‾Pen,obs,iPET‾Th,obs,i,
where PETcor,GCM,i and PETTh,GCM,i are bias-corrected annual PET and the
PET calculated from the Thornthwaite method, respectively, for the ith grid
point of the GCMs. PET‾Pen,obs,i and
PET‾Th,obs,i are the 49-year (1960–2008)
averages of PET calculated from the Penman and Thornthwaite methods, respectively,
for the ith grid point.
Based on the T data from the CRU, the Thornthwaite method is used to
calculate PET to test the applicability of Eq. (1). Figure 3 shows a
comparison of annual PET calculated from the Penman method and that from the
Thornthwaite method corrected by Eq. (1) during the period 1960–2008.
It is clear that the corrected PET agrees well with the PET from the Penman method,
with the correlation coefficients of 0.94 and 0.958 at the catchment and
grid scales, respectively. This suggests that Eq. (1) can be acceptable
for the bias correction of PET in the GCMs.
CMIP5 GCMs used in this study. The GCM data were statistically
downscaled and regridded onto a common 1∘× 1∘ global
grid from the Canadian Climate Data and Scenarios (CCDS).
No.ModelInstitution (country)Resolution1BCC-CSM1-1Beijing Climate Center, China Meteorological Administration,1∘× 1∘2BCC-CSM1-1-mChina3BNU-ESMCollege of Global Change and Earth System Science, Beijing1∘× 1∘Normal University, China4CCSM4National Center for Atmospheric Research, USA1∘× 1∘5CESM1-CAM5Community Earth System Model Contributors, USA1∘× 1∘6CNRM-CM5Centre national de Recherches Météorologiques/Centre1∘× 1∘Européen de Recherche et Formation Avancée en CalculScientifique, France7CSIRO-Mk3-6-0Commonwealth Scientific and Industrial Research Organization1∘× 1∘in collaboration with Queensland Climate Change Centre ofExcellence, Australia8CanESM2Canadian Centre for Climate Modelling and Analysis, Canada1∘× 1∘9EC-EARTHEC-EARTH consortium1∘× 1∘10FGOALS-g2LASG, Institute of Atmospheric Physics, Chinese Academy of1∘× 1∘Sciences and CESS, Tsinghua University, China11FIO-ESMThe First Institute of Oceanography, SOA, China1∘× 1∘12GFDL-CM313GFDL-ESM2GNOAA Geophysical Fluid Dynamics Laboratory, USA1∘× 1∘14GFDL-ESM2M15GISS-E2-HNASA Goddard Institute for Space Studies, USA1∘× 1∘16GISS-E2-R17HadGEM2-AONational Institute of Meteorological Research/Korea1∘× 1∘Meteorological Administration, South Korea18HadGEM2-ESMet Office Hadley Centre (additional HadGEM2-ES1∘× 1∘realizations contributed by Instituto Nacional de PesquisasEspaciais), UK19IPSL-CM5A-LRInstitut Pierre-Simon Laplace, France1∘× 1∘20IPSL-CM5A-MR21MIROC-ESMJapan Agency for Marine-Earth Science and Technology,1∘× 1∘Atmosphere and Ocean22MIROC-ESM-CHEMResearch Institute (the University of Tokyo), and NationalInstitute for Environmental Studies, Japan23MIROC5Atmosphere and Ocean Research Institute (The University of1∘× 1∘Tokyo), National Institute for Environmental Studies, and JapanAgency for Marine-Earth Science and Technology, Japan24MPI-ESM-LRMax-Planck-Institut für Meteorologie (Max Planck Institute for1∘× 1∘25MPI-ESM-MRMeteorology), Germany26MRI-CGCM3Meteorological Research Institute, Japan1∘× 1∘27NorESM1-MNorwegian Climate Centre, Norway1∘× 1∘28NorESM1-ME
Box plots of the simulation results of (a) mean annual T and
(b) mean annual P and the bias correction results of (c) mean
annual T and (d) mean annual P from 28 GCMs for the period 1971–2000
in the 14 river basins. The boxes denote the interquartile model spread (range
between the 25th and 75th quantiles), with the horizontal line indicating the
ensemble median and the whiskers showing the extreme range of the 28 CMIP5 model
simulations. The blue dotted lines denote the observed results of mean annual T
and mean annual P for the period 1971–2000. The basin number is consistent
with that given in Fig. 1.
Comparison of annual PET calculated from the Penman method and the
Thornthwaite method corrected by Eq. (1) during the period 1960–2008 for
(a) the 14 river basins and (b) all 0.5∘ grid points
over China.
Sensitivity of runoff to climate and catchment properties
The Budyko framework has been widely used to study basin-scale water and
energy balances. Two of the one-parameter formulations of the Budyko curve
proposed by Choudhury (1999) (Eq. 2; see also Yang et al., 2008) and
Fu (1981) (Eq. 3; see also Zhang et al., 2004) are expressed as
2E=PPETPn+PETn1/n,n∈(0,∞)3E=P+PET-Pω+PETω1/ω,ω∈(1,∞),
where n and ω are empirical parameters, representing the effects of
other factors (e.g. land surface characteristics, the average slope,
vegetation type or land use, and climate seasonality) on the water–energy
balance (Yang et al., 2008, 2014; Roderick and Farquhar, 2011; D. Li et al.,
2013). Yang et al. (2008) calibrated the parameters n and ω using
long-term water balance data from 108 catchments from the non-humid regions
of China and found that these two empirical parameters are linearly correlated.
Based on the Budyko hypothesis and assuming steady state conditions,
Roderick and Farquhar (2011) and Yang and Yang (2011) derived the elasticity
method to estimate the contribution to R from the changes in climate
(represented by P and PET) and catchment properties as follows:
dRR=εP⋅dPP+εPET⋅dPETPET+εn⋅dnn,
where εP, εPET, and
εn represent the elasticity coefficients of P, PET, and catchment
properties respectively and are expressed as
5εP=PR1-∂E∂P6εPET=-PETR∂E∂PET7εn=-nR∂E∂n,
where ∂E∂P, ∂E∂PET,
and ∂E∂n denote the first-order partial
derivatives of the Budyko equation with respect to P, PET, and the parameter n.
In this study, both Eqs. (2) and (3) are used for the estimation of
the elasticity of P, PET, and catchment properties over China.
Trend estimate method
The Mann–Kendall (M–K) non-parametric test (Mann, 1945; Kendall, 1975) is an
effective tool for detecting the statistical significance of trends in the
time series of meteorological and hydrological variables (Yang et al., 2014;
Wu and Huang, 2015). In this study, the M–K method is used to detect the
significance of monotonic trends in hydroclimatic time series. The
non-parametric trend slope estimator developed by Sen (1968) is used for the
magnitude estimation of the trends in a hydroclimatic time series.
ResultsInterannual variability of climatic variables and runoff
The standard deviations for annual P, PET, and R are computed for each of the
0.5∘ grids in China, and the PET deviation ratio (σPET/σP)
and the R deviation ratio (σR/σP) are
calculated. The spatial distributions of PET deviation ratio and
R deviation ratio across China are displayed in Fig. 4a and b. As
shown, the PET deviation ratio is rather small in most parts of China,
especially the southern regions, while a larger value is observed
mainly in the Xinjiang region, where there are greater aridity indices.
Generally, atmospheric water is enough to accommodate the limited PET in humid
climates, which would lead to a limited response of PET to P variability.
Specifically, the interannual variability of PET is more sensitive to that
of P in arid climates (with water limits) than in humid climates (with energy
limits). In contrast to the PET deviation ratio, the R deviation ratio tends to
increase from arid climates to humid climates. The reason for this is that,
in arid climates, the catchment water supply is very limited and gives
priority to evaporation and soil storage capability, which leads to little
variation in R.
Spatial distributions of (a) PET deviation ratio and
(b)R deviation ratio and (c) the relationship between
R deviation ratio and mean annual aridity index (ϕ‾) for all
0.5∘ grid points in China.
Figure 4c shows the relationship between the R deviation ratio and mean
annual aridity index (ϕ‾) for all 0.5∘ grids in China.
As indicated, ϕ‾ is a major control for the R deviation ratio
under not very dry conditions (e.g. ϕ‾< 10); that is,
the R deviation ratio decreases with increased ϕ‾. However,
under very dry conditions (e.g. ϕ‾> 10) the
R deviation ratio becomes insensitive to ϕ‾, since in this
case, other factors, such as soil storage capacity, can also have a large
impact on the variation of R.
Spatial distributions of the P elasticity of R across China from
(a) Eq. (2) and (b) Eq. (3). Spatial distributions of the PET
elasticity of R across China from (c) Eq. (2) and (d) Eq. (3).
Spatial distributions of the parameter elasticity of R across China from
(e) Eq. (2) and (f) Eq. (3).
Sensitivity of runoff to climate and catchment propertiesClimate elasticity
The P elasticity and PET elasticity of R based on Eqs. (2) and (3) are
estimated at each of the 0.5∘ grids in China. As shown in Fig. 5, the
spatial patterns of P elasticity and PET elasticity from Eqs. (2) and (3)
are almost the same in all regions of China. There is a large spatial
variation in P elasticity and PET elasticity, i.e. ranging from 1.1 to 3.2 and
from -2.2 to -0.1 across China, respectively. In particular, P elasticity is
more significant in the north-eastern and western areas than in southern China,
which is in contrast to PET elasticity. Figure 6 shows the relationship
between ϕ‾ and climate (P and PET) elasticity. As shown, the P (PET)
elasticity first increases (decreases) and then decreases (increases) with
the increase of ϕ‾ under not very dry conditions
(i.e. ϕ‾< 10). However, when ϕ‾ becomes
large enough (e.g. ϕ‾> 10), both P and PET elasticity
become insensitive to ϕ‾.
The climate elasticity estimated for each of the 14 large basins is shown in
Table 2. The values of P elasticity are in the range of 1.39–2.28, with a
larger (∼ smaller) elasticity in the Haihe River and Inner
Mongolia River (Southwest Drainage). A similar phenomenon is found for PET
elasticity, which suggests that Haihe River (Southwest Drainage) is the most
(least) sensitive to PET among the 14 basins. Overall the values of P elasticity
and PET elasticity derived by Eq. (2) are very close to those from
Eq. (3), but the difference between them tends to be larger for dry
basins with increasing aridity indices.
The estimations of P elasticity, PET elasticity, and catchment
properties' elasticity of R in the 14 river basins of China based on Eqs. (2)
and (3). The basin number is consistent with that given in Fig. 1. The numbers
in the parentheses indicate the 1960–2008 mean aridity index.
By using the estimates of climate elasticity derived by Eq. (2), the
change in R as a function of the percentage change in P and PET is calculated for
the 14 basins (Fig. 7). The R is positively related to P and negatively
related to PET, and the magnitudes and patterns of the response of R to changes
in P and PET vary on different scales. Generally, the R is more sensitive to
climate in the Haihe River and Inner Mongolia River, while relatively weak
sensitivity is found in the Southwest Drainage and Yangtze.
Catchment properties' elasticity
The spatial distributions of catchment properties' elasticity from Eqs. (2)
and (3) are displayed in Fig. 5e and f. As shown, the catchment
properties' elasticities for these two equations are rather similar across
China, and the values of Eq. (3) are generally smaller than those from
Eq. (2). Regarding the spatial pattern, the catchment properties'
elasticity is very weak (approximately equal to 0) in southern China and
some regions of north-eastern China, but it tends to be more significant in some
water-limited regions of north-west China. Figure 6c shows the relationship
between ϕ‾ and the parameter elasticity for all 0.5∘
grids in China. It suggests that ϕ‾ is a major control for
catchment properties' elasticity across China; i.e. the catchment properties'
elasticity would become stronger with increasing aridity indices. The
catchment properties' elasticities estimated for the 14 large basins are
shown in Table 2. The catchment properties' elasticity shows a large spatial
variation, ranging from -2.78 to -0.24 for Eq. (2) and from -4.3
to -0.33 for Eq. (3). Overall, the changes in R are more sensitive to
catchment properties in arid basins with larger aridity indices, which is
consistent with the findings at the grid scale.
Climate change during 1960–2008
The annual trend magnitudes in P, R, PET, and aridity index during the
period 1960–2008 are shown in Fig. 8a–d. As indicated, both
P and R show an increasing trend mainly in the north-west and south-east regions
and a decreasing trend mainly in the central region and the North China Plain. A
significant increasing trend in PET is detected mainly in north-eastern China and eastern
China, while the decreases mainly occur in most parts of western China. The
aridity index tends to show an increasing trend in most parts of China,
indicating an increasing risk of meteorological drought in these regions
during the past several decades. In contrast, the decrease of aridity index
is only found in some parts of western China.
The relationship between mean annual aridity index and (a)P elasticity,
(b) PET elasticity, and (c) parameter elasticity. The blue points
represent the case of Eq. (2), and the red points represent the case of Eq. (3).
Contour plot of percentage R change due to the changes in P and
PET for the 14 river basins. The P elasticity and PET elasticity of R are
estimated based on Eq. (2).
Trend magnitudes in annual time series of (a)P, (b)R,
(c) PET, and (d) aridity index for the period 1960–2008 and
spatial distributions of the contributions (unit: % yr-1) of (e)P,
(f) PET, and (g) climate (i.e. P and PET) to R in China
for the period 1960–2008. The trend magnitudes are estimated by Sen's method. Grey dots are shown as statistically significant positive/negative
trends (p< 0.05).
Changes in runoff due to climate change during 1960–2008
Using the estimates of climate elasticity from Eq. (2), the
contributions of P, PET, and climate (i.e. P and PET) to R in China for the
period 1960–2008 are calculated (as shown in Fig. 8e–g). A
positive contribution (up to 3.7 % yr-1) from P to R is mainly recorded
in western China, while a negative contribution is found mainly in north-eastern
China and the North China Plain. Negative and positive contributions of PET to R
mainly occur in north-eastern China and western China, respectively. The
contribution of climate, i.e. the sum of the contributions from P and PET,
ranges from -2.4 to 3.6 % yr-1 across China. The
spatial pattern of climate is rather similar to that of P, showing a negative
contribution in north-eastern China and a positive contribution in western China
and some parts of the south-east. In particular, the largest positive
contribution of climate occurs in the Tibetan Plateau. The contributions of
P, PET, and climate (i.e. P and PET) to R in the 14 river basins for the
period 1960–2008 are shown in Table 3. A positive contribution of P is detected in
Southeast Drainage, Southwest Drainage, Qiangtang, Qinghai, Xinjiang and
Hexi, while an opposite contribution is found in other basins. In contrast,
a negative contribution of PET is found in most of the basins (except for
Qiangtang and Hexi). In general, there is an increased R in Southeast
Drainage, Southwest Drainage, Qiangtang, Qinghai, Xinjiang, and Hexi (from
0.06 to 1 % yr-1) and a decreased R in other basins (from -1.12 to
-0.12 % yr-1).
Box plots of relative change (%) in mean annual P under (a) RCP2.6,
(b) RCP4.5, and (c) RCP8.5 scenarios and in mean annual PET
under (d) RCP2.6, (e) RCP4.5, and (f) RCP8.5 scenarios
calculated from 28 CMIP5 models in 14 basins for the period 2071–2100 (relative
to the baseline 1971–2000). The boxes denote the interquartile model spread
(range between the 25th and 75th quantiles), with the horizontal line indicating
the ensemble median and the whiskers showing the extreme range of the 28 CMIP5
model simulations. Red dotted lines denote the average values of the multi-model
ensemble. Blue dotted lines denote the 95 % significance levels' range of the
average values of the multi-model ensemble. The basin number is consistent with
that given in Fig. 1.
Future climate change
Figure 9 shows the uncertainty range of the relative change in mean annual P
and PET in the basins for the period 2071–2100 under the RCP2.6, RCP4.5, and
RCP8.5 scenarios as predicted by 28 CMIP5 models (relative to the
baseline 1971–2000). As shown, there is a large difference between different GCMs
and emission scenarios, which highlights the uncertainty inherent in
projections of climate change. However, overall P is projected to increase in
most of the basins, and greater increases are projected for higher emission
scenarios. Meanwhile, greater increases tend to be projected for more arid
basins, suggesting a decreasing risk of meteorological drought in the
future. The average changes (red dotted lines) of mean annual P for the
14 basins range from 2.4 to 11.0 % in RCP2.6, from 4.2 to 16.0 % in RCP4.5,
and from 3.1 to 23.7 % in RCP8.5. The largest
increase in the RCP2.6 and RCP8.5 scenarios is found for the Qinghai River,
while the largest increase in the RCP4.5 scenario is projected for the Hexi
River. For PET, there is an increase projected in all basins due to climate
warming, with the largest and smallest increases in the RCP8.5 and RCP2.6
scenarios, respectively. However, a large uncertainty exists among the GCMs,
which is similar to that for P. Furthermore, the uncertainty range tends to
be larger with higher emission scenarios. The average changes (red dotted
lines) of PET for the basins range from 7.0 to 12.0 % in RCP2.6, from
13.5 to 22.2 % in RCP4.5, and from 27.9 to 49.8 % in RCP8.5.
The largest and smallest average increases are projected for the Pearl River
and Qiangtang River, respectively.
The CMIP5 multi-model ensemble median relative change (%) in mean
annual P under (a) RCP2.6, (b) RCP4.5, and (c) RCP8.5
scenarios and in mean annual PET under (d) RCP2.6, (e) RCP4.5,
and (f) RCP8.5 scenarios in China for the period 2071–2100 (relative
to the baseline 1971–2000).
Figure 10 displays the multi-model ensemble median relative change in mean
annual P and PET in China for the period 2071–2100 (relative to the
baseline 1971–2000). The projected changes in P (or PET) have a similar spatial pattern
for the three emission scenarios; that is, P is projected to show an increase
in western China and the north-east, and PET is projected to increase
significantly in southern China and some parts of the Tibetan Plateau,
especially for the RCP8.5 scenario. In addition, note that there are small
changes in P and significant increases in PET projected for southern China. This
would result in an increasing risk of meteorological drought in the future.
Future changes in runoff due to climate change
Based on the estimates of elasticity from Eq. (2), the percentage
changes in the contributions of annual P and PET, as well as climate, to R from
the 28 GCMs for the period 2071–2100 are calculated for each of the
14 basins (relative to the baseline 1971–2000). As shown in Fig. 11, the
changes in P contribution mainly follow the changes in P itself (Fig. 9). A
positive contribution from P is projected for most of the basins, and larger
contributions occur in more arid basins, as well as in higher emission
scenarios. Negative contributions of PET to R are projected for all basins due to
the negative coefficients of PET elasticity. Smaller contributions of PET are
mainly found in the Southwest Drainage. In contrast, larger contributions
are projected mainly in the Huaihe River, Haihe River, and Inner Mongolia
River, where the percentage decreases from the 28 models can be up to 25, 35,
and 90 % in the RCP2.6, RCP4.5 and RCP8.5 scenarios, respectively.
Climate change is projected to reduce the R in some humid basins, such as the
Southeast Drainage and Pearl River, where the average changes in the three
emission scenarios range from -22.83 to -3.0 % and from -23.6 to
-3.5 %, respectively (Fig. 11g–i). For other basins,
particularly for arid basins, the R is projected to increase due to climate
change. The largest average changes in R under the RCP2.6 and RCP4.5
scenarios are found in the Qinghai River (12.85 and 16.18 %,
respectively). For the RCP8.5 scenario, they are found in the Qiangtang
River (18.59 %). Note that there is an obvious decrease in R (-17.59 %)
projected for the Huaihe River under the RCP8.5 scenario, which is mainly caused
by the larger negative contribution of PET.
Box plots of relative change (%) in the contributions of annual P
to R under (a) RCP2.6, (b) RCP4.5, and (c) RCP8.5
scenarios, in the contributions of annual PET to R under (d) RCP2.6,
(e) RCP4.5, and (f) RCP8.5 scenarios, and in the contributions
of climate to R under (g) RCP2.6, (h) RCP4.5, and
(i) RCP8.5 scenarios calculated from 28 CMIP5 models in 14 basins for
the period 2071–2100 (relative to the baseline 1971–2000). The boxes denote
the interquartile model spread (range between the 25th and 75th quantiles), with
the horizontal line indicating the ensemble median and the whiskers showing the
extreme range of the 28 CMIP5 model simulations. Red dotted lines denote the
average values of the multi-model ensemble. Blue dotted lines denote the 95 %
significance levels' range of the average values of the multi-model ensemble.
The basin number is consistent with that given in Fig. 1.
The CMIP5 multi-model ensemble median relative change (%) in the
contributions of annual P to R under (a) RCP2.6, (b) RCP4.5,
and (c) RCP8.5 scenarios, in the contributions of annual PET to R
under (d) RCP2.6, (e) RCP4.5, and (f) RCP8.5 scenarios,
and in the contributions of climate to R under (g) RCP2.6,
(h) RCP4.5, and (i) RCP8.5 scenarios in China for the
period 2071–2100 (relative to the baseline 1971–2000).
The contributions of P, PET, and climate (i.e. P and PET) to R
in the 14 basins of China for the period 1960–2008. The basin number is
consistent with that given in Fig. 1. The numbers in the parentheses indicate
the 1960–2008 mean aridity index.
Figure 12 shows the spatial distributions of the relative changes in the
contributions of annual P and PET as well as climate to R in China for 2071–2100.
This is based on the CMIP5 multi-model ensemble medians. Compared with the
baseline 1971–2000, the increases in R due to the changes in P are projected
in western China and some parts of northern China, and this phenomenon is
particularly significant in the RCP8.5 scenario (up to 60.3 %). In
contrast, the changes in PET are projected to reduce the R in all of China, with
the larger decreases occurring mainly in the North China Plain, north-eastern China,
and some parts of western China. Overall, climate change is projected to
cause an obvious increase (decrease) of R in western China (southern China)
under any emission scenario (Fig. 12g–i). This suggests that the arid regions
(humid regions) in China will become wetter (drier) in the future.
DiscussionThe estimation of elasticity
The Budyko-based elasticity method is applied to quantify sensitivity of
runoff to climate and catchment properties across China. Two Budyko models
proposed by Choudhury (1999) and Fu (1981) are used for the comparison of
the estimation of the climate elasticity of R. The results suggest that the
climate elasticity is insensitive to the Budyko equations. The climate
elasticity of R has been estimated in many regions of China. For example, the
values of P elasticity are estimated as 2.4 for the Miyun Reservoir basin (Ma
et al., 2010), 2.6 for the Luan River basin (X. Y. Xu et al., 2013), 2.1 for the
headwater catchments of the Yellow River basin (Zheng et al., 2009),
1.4–1.7 for the Poyang Lake basin (Sun et al., 2013), 1.7–3.1 for the Hai
River basin (Xu et al., 2014), 1.1–2.0 for southern China, the Songhua
River basin, and the north-west, 2.1–4.8 for the Hai River basin, the Yellow
River basin, and the Liao River basin (Yang et al., 2014), and 1.6–3.8 for
the 63 catchments of China (Yang and Yang, 2011). In addition, the PET
elasticity is estimated as -1.04 for the headwater catchments of the Yellow
River basin (Zheng et al., 2009) and from -1 to -0.2 for the Poyang Lake
basin (Sun et al., 2013). Those results are close to our results for
P elasticity ranging from 1.1 to 3.2 and for PET elasticity ranging from -2.2
to -0.1 in China. It is worth noting that the values of P elasticity tend to be
larger in the north-eastern and some parts of western China that are located in
arid climates. This is in good agreement with the findings by
Sankarasubramanian et al. (2001), which indicated that a larger P elasticity
occurs in more arid regions. However, some parts of Xinjiang, which is more
arid than southern China, have smaller P elasticity. Meanwhile, some parts of
southern China, which is more humid than other regions in China, have larger
P elasticity (Fig. 5). In addition, the Haihe River basin, located in a less
arid climate than that of the north-west, shows the largest P elasticity in
China (Table 2). A similar phenomenon is also introduced in Yang et al. (2014).
One of the major reasons for this difference may be attributed to
the impacts of human activities that alter the patterns of R in these
regions. In addition, uncertainties in water budget data, such as the errors
in the simulation of R and in the estimation of PET, may also contribute to this difference.
The comparisons for the estimates of εn and εω
suggest that although the values of εn and εω
are mainly dependent on the parameters of
Budyko models, the spatial pattern of εn is consistent
with that of εω at the 0.5∘ grid points over
China (Fig. 5e and f). Yang et al. (2008) indicated that the
parameters n and ω from Eqs. (2) and (3) are linearly correlated.
We also conducted a regression analysis of εn and εω
for all 0.5∘ grid points over China
and found a strong linear correlation between εn and
εω(εω= 1.7061εn+ 0.0986, r2= 0.96). In
addition, our results show that R is more sensitive to catchment properties
(εn and εω) in the more arid
regions (Fig. 5e and f). The possible internal connection is that the
arid regions with less vegetation coverage and stronger evaporation do not
effectively hold the rainfall water that will be evaporated, leading to the
smaller proportion of rainfall for R.
(a) Mean annual PET calculated from the four methods for the
14 river basins of China during the period 1960–2008. (b) PET elasticity
calculated from Eq. (2) based on the four PET data for the 14 river basins of
China during the period 1960–2008. The basin number is consistent with that
given in Fig. 1.
Sensitivity analysis for PET calculation methods
We compare four PET calculation methods, including the Penman method, the
Thornthwaite method, the FAO-56 Penman–Monteith method (Allen et al.,
1998), and the Thornthwaite method corrected by Eq. (1), to test the
robustness of the PET elasticity result subject to PET uncertainties. In terms of
mean annual PET as shown in Fig. 13a, the Thornthwaite method gives
relatively low PET among the four methods, especially in arid basins (e.g.
Qiangtang, Qinghai, Xinjiang, and Hexi). This is in agreement with previous
studies, which indicated that the Thornthwaite method tends to underestimate
PET in the arid areas (Hashemi and Habibian, 1979; Malek, 1987; Garcia et al.,
2004). In contrast, the mean annual PET values from the other three methods are quite
consistent, especially the Penman method and the Thornthwaite method
corrected by Eq. (1). A similar result was also reported by Zeng and
Cai (2016), which indicated that estimations of water balance at both annual
and month scales are generally robust under various PET calculation methods
(not including the Thornthwaite method). The PET elasticity calculations from
the four different PET data for the 14 river basins are shown in Fig. 13b.
The Thornthwaite method yields stronger PET elasticity than the other three methods
in most of the basins, mainly due to the underestimation of PET. However, the
other three methods give very similar results in all 14 basins. In summary,
the estimation of PET elasticity is robust according to the PET calculations from the Penman
method, the FAO-56 Penman–Monteith method, and the Thornthwaite method
corrected by Eq. (1) but is not acceptable for the Thornthwaite method itself.
In general, the Thornthwaite method corrected by Eq. (1) significantly
improves the accuracy of PET (Figs. 3 and 13a). However, it should be
emphasized that the Thornthwaite method is an empirical equation that
neglects the effects of atmospheric conditions, such as wind speed, humidity
and radiation (McVicar et al., 2012). In addition, Eq. (1) used for
the bias correction of PET is part of a delta method (Graham et al., 2007;
Sperna Weiland et al., 2010), which only considers the average change but
ignores the differences in the standard deviation and the coefficient of
variation between the projection and baseline periods (Watanabe et al.,
2012). Therefore, a more physically based PET calculation method (such as the
Penman method) needs to be considered to fully understand the PET calculation
uncertainties in the projections of climate change.
The projections of climate change and runoff
The hydrological impacts of climate change have been investigated in many
regions of China, such as the Hanjiang basin (Chen et al., 2007; Guo et al.,
2009), the catchment of the Loess Plateau (Wang et al., 2013), the Qingjiang
River basin (Chen et al., 2012), the Qiantang River basin (Y. P. Xu et al.,
2013), the Songhuajiang River basin (Su et al., 2015), the south-eastern
Tibetan Plateau (F. Li et al., 2013), the Pearl River basin (Yan et al.,
2015), the Xin River basin (Zhang et al., 2016), the subcatchments of the
Yangtze and Yellow River basins (Xu et al., 2011), the Huang-Huai-Hai region
(Lu et al., 2012), and 10 major river basins in China (Wang et al., 2012).
There is a large uncertainty involved in these impact studies, which results
in a large difference in climate projections. For example, Wang et al. (2012)
indicated that the prevailing pattern of “north dry and south wet”
in China will likely be exacerbated under future climate warming. However,
the results of most GCMs in this study suggest that the arid regions and
humid regions of China are projected to become wetter and drier in the
future, respectively. The main difference between the two studies is the use
of different climate models, emission scenarios, and time periods. This also
demonstrates that the results of climate projections should be taken with
caution, since the regional climate simulations (especially of
precipitation) from the GCMs are still not robust at the present stage.
This study focuses on the hydrological change due to climate change (i.e.
changes in P and PET), while the effects of the variability of catchment
properties (e.g. land cover change, groundwater and river water extraction,
urbanization, irrigation) on the hydrology are overlooked here. Most
of the available GCMs lack key regional feedback processes involving land
use, such as forest plantations, irrigation, and urbanization feedbacks that
are critically important throughout China (Piao et al., 2010). The projected
changes in catchment properties therefore need to be involved in the GCMs to
account for their hydrological impacts. In addition, recent studies
indicated that plant responses to increasing CO2 tend to keep more
water on land, hence resulting in a greater increase in R (Milly and Dunne,
2016; Swann et al., 2016); that is to say, the hydrological models (e.g. VIC
model), without the schemes of the plant stomatal responses to CO2,
would lead to an underestimation of R under high CO2. Therefore, the
implications of plants needing less water under high CO2 should be
included in the assessment of hydrological impacts of climate change.
Uncertainties
Generally, a multitude of sources of uncertainty are involved in the impact
assessment of climate change. In this study, uncertainty mainly comes from
the GCMs, emission scenarios, the elasticity method, and the estimation
error of the water budget data. To highlight the uncertainty from the GCMs,
the 28 GCMs, as produced by different research institutes around the world,
are used for the comparison of climate change projections. There is a
large difference in the projections of P and PET among the 28 GCMs.
In particular, the uncertainty range of P tends to be larger for more arid
regions, while the uncertainty range of PET tends to be larger for more humid
regions (Fig. 9). This highlights the impact of potential misleading
conclusions if only one climate model were to be used for the impact
assessments. The large uncertainty driven by the GCMs in relation to the
hydrological impacts of climate change has been reported in many previous
studies (Kay et al., 2009; Prudhomme and Davies, 2009; Chen et al., 2011;
Teng et al., 2012; Liu et al., 2013; Wu et al., 2014, 2015). It is worth
noting that although the projected ranges of P and PET show large variability in
various GCMs, most project a consistent change (i.e. increase) in P and PET for
the future period (Fig. 9). In contrast, the uncertainty from the emission
scenarios is smaller than that from the GCMs, since the projected changes
in P (or PET) show a similar pattern under all emission scenarios (Fig. 9). The
main difference is that the projected changes tend to be more significant in
higher emission scenarios.
The elasticity equation (i.e. Eq. 4) used in this study is driven
from the linear approximation of the Budyko equation (Eqs. 2 and 3)
by neglecting the higher order. Such approximation would possibly lead to
uncertainty in the estimation of climate elasticity. Yang et al. (2014)
indicated that the error in the estimation of elasticity tends to increase with
increasing changes in P and PET, as well as the increased parameter of the
Budyko equation. Future research is needed to quantify the effects of the
errors on the estimation of elasticity under various climate conditions.
In addition to uncertainty in PET calculation (as discussed in Sect. 4.2),
there are also uncertainties associated with the estimates of other water
budget components, such as R. As shown in Fig. 14, the sensitivity of
climate (i.e. P and PET) elasticity to R varies considerably between basins and
tends to be larger in more humid basins. Moreover, PET elasticity is more
sensitive to changes in R compared with P elasticity for all 14 basins. As
indicated by Zhang et al. (2014), although the R is realistically estimated
for most of the basins (especially for humid basins) in China with a small
relative error, there is still a large relative error for few arid basins in
western China due to the lack of meteorological observations. Therefore, the
large errors in simulated R of the VIC model may result in large
uncertainties in the elasticity calculation, particularly in western China. Also
note that some other natural water sources, such as snow and glaciers, which
may contribute to R, are overlooked in this study. Lute and Abatzoglou (2014)
highlighted the importance of extreme snowfall events in shaping the
interannual variability of the water balance. The melting of snow and
glaciers is generally significant at a seasonal timescale in some high-altitude regions of China. Neglecting the effects of snow and glaciers would
lead to a bias in the modelling of R for these regions.
Comparison of changes in (a)P elasticity and (b) PET
elasticity in response to changes in R for the 14 river basins of China. The
basin number is consistent with that given in Fig. 1.
Conclusion
In this study, the Budyko-based elasticity method was used to investigate
the responses of runoff to historical and future climate variability over
China at both grid and catchment scales. The climate and catchment
properties' elasticities of runoff were estimated based on the long-term (1960–2008)
land surface data from Zhang et al. (2014). Twenty-eight GCMs
with three emission scenarios from the CMIP5 were collected for the
projections of climate change and its contribution to runoff in China during
the period 2071–2100. The uncertainties associated with the estimates of
PET, R, and climate elasticity, as well as climate projections, are discussed in
detail. The main findings are summarized as follows.
The interannual variability of PET is more sensitive to that of P in more
arid regions, while the opposite occurs in the response of interannual
variability of R to that of P. A large spatial variation exists in P elasticity
(from 1.1 to 3.2) and PET elasticity (from -2.2 to -0.1) across China. The
P elasticity is larger in north-eastern and western China than in southern China,
which is opposite to that of PET elasticity. Among the 14 river basins, the
Haihe River and Southwest Drainage have the largest and smallest climate
elasticities, respectively. The catchment properties' elasticity of R is
sensitive to mean annual aridity indices and tends to be stronger in more
arid regions with increasing aridity indices.
For the period 1960–2008, the positive (negative) contributions from P
to R are mainly found in western China (north-eastern China and the North China Plain),
and the positive (negative) contributions of PET mainly occur in western China
(north-eastern China). Overall, the climate contribution to R ranges from
-2.4 to 3.6 % yr-1 across China during the period 1960–2008,
with a negative contribution in north-eastern China and a positive
contribution in western China and some parts of the south-west. The largest
positive and negative contributions of climate occur in the Qiangtang and
Haihe River basins, respectively.
There is a large uncertainty in climate projections among the 28 GCMs.
Moreover, the uncertainty range of the P (PET) projection tends to be larger for
more arid (humid) regions. However, most of the GCMs project a consistent
change in annual P or annual PET. For the period 2071–2100, the P is projected
to increase in most parts of China, especially the western regions, and the
PET is projected to increase in all of China, particularly the southern
regions. Furthermore, greater increases are projected for higher emission
scenarios. Due to future climate warming, the arid regions and humid regions
of China are projected to become wetter and drier in the period 2071–2100,
respectively (relative to the baseline 1971–2000).
The results of this study (especially of the climate change projections)
should be taken with caution, since uncertainties in the results exist
because of several issues, including the different simulations of GCMs, the
estimation error of climate elasticity, and the estimation error in the
water budget components. A thorough investigation of the uncertainty
involved in the hydrologic effects of climate change in China should be
considered in future research.
Data availability
The PET data are provided by the Terrestrial Hydrology Research
Group of Princeton University (http://hydrology.princeton.edu/data.php;
Sheffield et al., 2006, 2012). The land surface data over China, including P,
RS, and BS, are provided by the Land Surface Processes and Global Change Research
Group (http://hydro.igsnrr.ac.cn/resources.html; Zhang et al., 2014). The
CMIP5 GCM data are obtained from the Canadian Climate Data and Scenarios (CCDS, http://climate-scenarios.canada.ca/?page=main).
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
This research was supported by the Fundamental Research Funds for the
Central Universities (grant no. 21617301) and partly supported by funding
from the National Natural Science Foundation of China (grant no. 41530316)
and the National Key Research and Development Program of China (grant
no. 2016YFC0402805). We thank the editors and two reviewers for their valuable
comments that considerably helped to improve this paper.
Edited by: Jim Freer
Reviewed by: Simon Dadson and one anonymous referee
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