Modelling Hydrological Ecosystem Services of native forest for Integrated Water Resources Management on a poorly monitored basin of Central Chile

Ecosystem goods and services (BSE) of native forest are fundamental for water supply in Central Chile. The ongoing Megadrought (MD)- a decade lenght below normal precipitation years (~30-40%)- that affects the region, has exacerbated the water scarcity, generating a favorable scenario for the systematization and structuring of Payment for Ecosystem Services (PES) schemes in Mediterranean-climate basins of Chile. Hydrological modeling tools can be useful to support collaborative decision processes needed to implement these PES, as well as water management adaptation plans. In this context, the Chilean Water Directorate is leading the implementation of Basin Scale Strategic Water Management Plans (BSWMP) using the Water Evaluation and Planning Model (WEAP). However, the lack of biophysical data in poorly monitored basins, challenge the model implementation to quantify these ecosystem services. In this research, we used satellite data, which combined with short term field data allow us to represent the climate-forest-hydrological feedbacks and to quantify the water related ecosystem services at the sub-basin scale in the Aculeo Lake catchment, an iconic agricultural basin located in the Metropolitan region of Chile. The results indicate that there is significant impact of the MD in the native forest of the Aculeo basin, revealed by decreases in the normalized difference vegetation index and the leaf area index (~50% since year 2019), which translate into reduced evapotranspiration values. Also, according to the hydrological model, the native forest ecosystem services exacerbated during the MD, leading to increased surface runoff, infiltration rates and lake water volume storage, revealing its key role on the hydrological system. Finally, a modelling framework has been designed to support the WEAP model implementation to simulate and quantify the native forest ecosystem services at the basin scale, for poorly gauged basins, in the context of the current BSWMP.