Towards a complete Himalayan hydrological budget : The spatiotemporal distribution of 1 snowmelt and rainfall and their impact on river discharge

7 The hydrological budget of Himalayan rivers is dominated by monsoonal rainfall and 8 snowmelt, but their relative impact is not well established. Current knowledge of rainfall and 9 snow-cover distribution is unreliable because this remote region lacks a dense gauge network. 10 Here, we use a combination of remotely-sensed climate parameters that have been both 11 calibrated and validated to characterize the spatiotemporal distribution of rainfall, snowfall, and 12 evapotranspiration in order to quantify their relative contribution to mean river discharge. 13 Rainfall amounts are calculated from explicitly calibrated, orbital, high-resolution (~5x5 km) 14 TRMM (Tropical Rainfall Measurement Mission) data, and snow-water equivalents are 15 computed from a snowmelt model based on satellite-derived snow cover, surface temperature, 16 and solar radiation. Despite complex hydrological interactions, we are able to hindcast river 17 flows within 5% of their monthly measured values from a river-gauge network with daily 18 measurements spanning the entire Himalaya. Our data allow us to identify five key aspects of the 19 spatiotemporal precipitation pattern. First, we observe a strong decoupling between the rainfall 20 on the Himalayan foreland versus that in the mountains: a pronounced 6-fold, east-west rainfall 21 gradient in the Ganges plains exists only at elevations < 500 m asl. Mountainous regions (500 to 22 5000 m asl) receive nearly equal rainfall amounts along strike, such that the overall rainfall 23