Dataset and code from: Persistent loss of rainfall–runoff efficiency in a strategic tropical hydropower watershed

Monthly time series of precipitation (CHIRPS Pentad v2.0), actual evapotranspiration (MODIS MOD16A2 v6.0), simplified water balance and observed reservoir inflow (SAR/ANA) for the Furnas Reservoir watershed (51,950 km²), upper Grande River, Minas Gerais, Brazil, covering January 2001 to December 2021 (n = 252 months). Includes the Google Earth Engine script used to derive the orbital series, the statistical analysis code (Mann-Kendall, Pettitt, Mann-Whitney U), the figure generation code, and the aggregated seasonal and annual series with evaporative index and runoff coefficient. Supporting data for the article of the same name.