Climate change has disastrous consequences for the natural water cycles in South Asia and the Indus basin, leading to frequent floods and droughts, elevated food & energy insecurity, and the depletion of critical water resources. For communities, the availability of timely information about uncertain hydrometeorological variables has become extremely important for achieving high crop water productivity, signaling the onset of heatwaves, and the early warning of floods & droughts. Hidden state variables such as soil moisture, snow depth, and local meteorology provide critical insights for attributing extreme events to climate change. In light of these needs, we summarize our work on indigenously building large-scale earth observation networks using a fusion of many technologies and with the participation of communities. This presents many opportunities for systems thinking. Our data-collection efforts, combined with agent-based socio-hydrological models and basin-scale integrated assessment models have enabled large-scale policy interventions for irrigation demand management, the exploration of nature-based solutions in agriculture, preparation for rare events in transboundary rivers, and generation scenarios for investment options in the Water-Energy-Food-Climate nexus.