The High Mountains of Asia, i.e., the Third Pole, are among the most important water reserves in the world because of the downstream dependency, for both direct human consumption and food production, on the upstream glaciers and snow. With changing climate and subsequent alteration of snow and glacier dynamics, the region has already been identified as one of the most vulnerable, necessitating detailed understanding of the impacts of these changes. Moreover, the trajectory of socio-economic development will also play a crucial role in the interplay between future water availability, demand, and food production. As such, with the aim of quantifying the consequences of both climate change and socio-economic development in the Third Pole region at a high spatial and temporal resolution, here we couple the widely used Spatial Processes in HYdrology (SPHY) model with the Lund-Potsdam-Jena managed Land (LPJmL) model. The idea behind this one-way coupling is to improve upon the poorly represented cryosphere processes in the latter by using the SPHY model outputs from the upstream mountain sub-basins while concurrently simulating the downstream hydrology, irrigation and crop growth with LPJmL. The coupled model further incorporates spatially explicit representation of multi-cropping, along with the extensive irrigation and inter-basin transfer canals for a realistic modeling of local agriculture and irrigation. As a first application result, an initial assessment of the importance of meltwater in different parts of the region and the contribution of mountain water to irrigated agriculture is presented. An overview of the current spatio-temporal status of water availability, demand and use, along with the crop-specific water requirement and yield is also provided. Future applications of the model are expected to increase our understanding of the diverse upstream-downstream relationships over the Third Pole region and help support adaptation design through the identification of vulnerability hotspots in different basins.