Streamflow regimes are rapidly changing in many regions of the world. The ability to attribute these changes to specific hydrological processes and their underlying climatic and anthropogenic drivers is essential to formulate effective water policy. Traditional approaches to hydrologic attribution rely on the ability to infer hydrological processes through the development of catchment-scale hydrological models. However, such approaches are challenging to implement in practice. In particular, models have difficulty capturing hydrological regime shifts, where changes in the dominant hydrological processes alters the relationship among hydrological fluxes. Additionally, observational uncertainties might preclude closure of the catchment-scale water balance, which is a pre-requisite for most catchment-scale hydrological models. Here we present an alternative approach to hydrological attribution that leverages the method of multiple hypotheses. We generate and empirically evaluate a series of alternative and complementary hypotheses that pertain to hydrological change. These hypotheses concern distinct components of the water balance and are evaluated independently. This process allows a holistic understanding of watershed-scale processes to be developed, even if the catchment-scale water balance remains open. We apply the approach to understand changes in the Upper Jhelum river, an important tributary headwaters of the Indus basin, where streamflow has declined dramatically since 2000 and has yet to be adequately attributed to its corresponding drivers. Using remote sensing and secondary data collected from the watershed, we explore changes in climate, surface water, and groundwater. The evidence reveals that climate, rather than land use, had a considerably stronger influence on reductions in streamflow, both through reduced precipitation and increased evapotranspiration.
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