While rainfall reduction is the main driver, increased temperature and evaporation can also play a role. Another influence on drought severity is the condition of the catchment area where rain falls and drains into rivers. Important factors here include the amount and type of vegetation covering the catchment and soil characteristics.
Water flowing from these catchments is captured and stored in six large dams. During the drought, dam levels dropped to less than 20% of their capacity. Our analysis aimed to see whether clearing alien trees from these mountain catchments would have lessened the impacts of lower rainfall from climate change on river flows. Using climate models and a hydrological model we simulated worlds with and without human-driven climate change and with and without catchment restoration and maintenance.