Water fluxes under threat by changes in land cover and climate in the Brazilian Cerrado biome

In developing countries, the economy is commonly based on agriculture, and combined with the demand for the expansion of urban centers, large natural territories have been converted into agricultural and urban areas. In Brazil, the productive engine for agricultural activities is mainly situated in the wooded Cerrado biome, which has undergone agricultural expansion that led to almost 50% of the native forest vegetation. Besides being well know the role land cover plays on water fluxes, there is still requirement to further coupling with climate change component. The predicted alteration of climate patterns under future climate change scenarios can potentially alter infiltration/runoff rates, aquifer recharge, and soil-water availability for plants, impacting plant growth and development. In this research, we evaluated changes in water fluxes (surface flux, evaporation, soil-water storage, infiltration, bottom flux, and root uptake) at intermediate (2040-2070) and distant future (2071-2100) due to climate change occurring in the Brazilian Cerrado Biome. The two specific objectives included the calibration and validation of the Hydrus model through an eight-year soil moisture monitoring on experimental plots in Cerrado, pasture, and sugarcane areas (i), as well as the incorporation of outcomes from climate change models (10 CMIP6 models under SSP2-4.5 and SSP5-8.5 scenarios) into the validated Hydrus models (ii). The predicted water fluxes were made by Hydrus, a computational that uses the finite element method to achieve the numerical solution of the Richards Equation to describe saturated/unsaturated flows. The study is composed of experimental plots (100 m² and 9% slope) with weather variables and soil moisture fluctuations from 2011 to 2018. We tested different parameter combinations during calibration and found that for sugarcane and pasture simulations plots, saturated soil water content, parameter N in the soil retention function, and saturated hydraulic conductivity were the most sensitive ones and led to better calibration statistics. The first observation is that we cannot point out that climate change is affecting preferentially superficial fluxes rather than sub-superficial ones since each variable has a singular behavior under climate scenarios. Nonetheless, climate change poses a higher threat to certain water fluxes than others, being at a hierarchical (bottom-top) sequence: soil-water storage, bottom flux, infiltration, surface flux, evaporation, and root uptake. The same sequence is applied to all land cover, differing in magnitudes. Comparing the actual water fluxes due changes in to land cover with those due to climate, we concluded that the intensification of land cover change poses a higher risk of water fluxes than those predicted due to climate change. The intricate relationship between land cover and climate necessitates a nuanced understanding to anticipate and mitigate the consequences on water fluxes.