20 Feb 2020
20 Feb 2020
Status: this discussion paper is a preprint. It has been under review for the journal Hydrology and Earth System Sciences (HESS). The manuscript was not accepted for further review after discussion.

Infiltration-Friendly Land Uses for Climate Resilience on Volcanic Slopes in the Rejoso Watershed, East Java, Indonesia

Didik Suprayogo1, Widianto1, Kurniatun Hairiah1, Nabilla Meilasari1, Abdul Lathief Rabbani1, Rizky Maulana Ishaq1, and Meine van Noordwijk1,2,3 Didik Suprayogo et al.
  • 1Soil Science Department, Faculty of Agriculture, Brawijaya University, Jl. Veteran no 1, Malang 65145, Indonesia
  • 2World Agroforestry Centre, ICRAF, Indonesia Office, Bogor, Indonesia
  • 3Plant Production Systems, Wageningen University, Wageningen, the Netherlands

Abstract. Forest conversion to agriculture or agroforestry may increase risks of loss of hydrologic functions in an era of climate change. Infiltration during high-intensity rainfall is important for avoiding erosion and feeding aquifers but depends on land use practices that maintain soil macroporosity. In the forest-to-open-field-agriculture continuum it is not clear where thresholds to functionality (degradation) are crossed. Our assessment of infiltration-friendly land uses in the Rejoso watershed on the slopes of the Bromo volcano in East Java (Indonesia) focused on two zones, upstream (above 800 m a.s.l.) and midstream (400–800 m a.s.l.) of the Rejoso river and feeding aquifers that support lowland rice areas as well as drinking water supplies to nearby cities. Upstream land uses included old and young pine plantations (production forest) and highland vegetable crops with variation of tree canopy cover. Midstream land uses included production forest, multistrata coffee-based agroforestry, clove-based agroforestry, and several mixed agroforestry types with variation of tree canopy cover. We quantified infiltration and erosion in 3 replications per land use category over a 3-month period (one-third of mean annual rainfall), with 6–13 % of rainfall with intensities (51–100 mm day−1). We related infiltration rates to plot-level characteristics across the land use systems and found statistically significant relations with tree canopy cover (likely based on combined effects of interception, preceding water use and effects on soil), understory cover, amount of litter, and soil surface roughness. Results for the upstream watershed showed that a tree canopy cover > 55 % is associated with adequate infiltration and acceptable soil erosion levels. For vegetable cultivation in steep (45–65 %) to very steep (> 65 %) lands with a tree canopy cover below 55 %, surface runoff was between 24 % and 46 % of rainfall, with high rates of soil erosion. Midstream, a tree canopy cover of > 80 % was associated with infiltration-friendly land use, given the higher rainfall total (and rainfall intensity) in this zone. For a tree canopy cover in the range 20–80 %, erosion rates were relatively low, but surface runoff increased to 36 to 62 % of rainfall. Differences in soil type influenced the thresholds, as the areas’ Inceptisols have lower intrinsic porosity than Andisols. A high soil surface roughness and litter thickness assist in reducing surface runoff and soil erosion. Where more open forms of agroforestry, with tree canopy cover less than 80 % are becoming more common this will affect water resources in the downstream area and increase vulnerability to climate change.

Didik Suprayogo et al.

Didik Suprayogo et al.

Didik Suprayogo et al.


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Short summary
In SDG 6, water access for all is agreed, not only refers to drinking-water but also requires the protection upland watersheds. However, forest conversion is still rapid happen. This conversion may increase loss of hydrology functions in an era of climate change. We quantified infiltration and soil erosion in the natural rainfall. The infiltration rates found significant relations with tree canopy cover and litter thickness. This research is an important to support environmental service program.