Humans  activities are today’s major geophysical forces driving the Earth’s environmental changes. Over the past century, humans have altered various Earth system processes over a broad range of scales resulting in profound and often unprecedented negative environmental consequences, and freshwater systems are one of the most altered ecosystems. It is now well recognized that the water cycle is not natural anymore. Some of the most prominent and plainly visible impacts on freshwater systems are the changes in natural flow regimes, disappearance of large surface water bodies such as the Aral sea, and widespread depletion of groundwater resources around the world. On the one hand, the water cycle is continually changing in response to natural climate variability (climate change), and on the other hand, increasing human appropriation of freshwater systems is exerting additional pressure on already scarce water resources. Collectively, these issues have raised serious concerns about global water resources sustainability and food security for the foreseeable future.

Sustainable management of these resources requires accurate assessment and reliable future projections. Hydrological models are essential tools for such estimation and future projection of water resources availability. Unfortunately, most large-scale hydrological models and global climate models still simulate only the natural water cycle without considering the human activities which are the major driving forces. Therefore, the hydrologic and climate research community still lacks holistic and integrated models for simulating human impacts on the water cycle at the global scale and also for accurately predicting future impacts. Recognizing this gap, we are developing large-scale hydrological models that can simulate both the natural and human-induced changes in the water cycle, and can be used to monitor the terrestrial water cycle and thereby contribute toward finding sustainable solutions for adequate supply of water and food for the burgeoning population in the world. In my previous publications, I have sought to answer part of the following question that constitutes my professional goal: “How did humans affect the global water cycle in the past and how will the water cycle change in the future in the context of increasing water demand due to escalating global population and changing global climate?” by using an integrated hydrological model developed through the incorporation of major human factors such as irrigation, damming, and groundwater pumping into a global climate model. We are currently working on the improvement of the developed model, particularly to: incorporate more realistic groundwater flow processes such as lateral groundwater convergence, account for inter-grid water transfer, increase model-grid resolution and develop a high-resolution regional model for North America, and predict future impacts and climate feedbacks.

Our professional goal is to seek a better understanding of the broader consequences when the human factors are combined with global climate change, through the representation of these human factors in climate and Earth Systems Models. As the evidence of the negative consequences of growing human effect on the Earth keep growing, the hydrologic research community is increasingly aware that the representation of human impacts in models is extremely important. However, even as the global population and consequent stress on water resources dramatically increase, the hydrologic and climate research community is yet to develop the holistic and integrated large-scale models for simulating human impacts on the water cycle and for accurately predicting future impacts. As such, our research seeks to develop global and regional models for monitoring the terrestrial water cycle and thereby contribute toward finding sustainable solutions for adequate supply of water and food for the burgeoning global population. We seek to answer the following broad but closely inter-related key scientific questions:

  1. Understanding the Hydrologic Cycle: What is the current state of understanding of the global hydrologic cycle in the context of growing human interventions? What are the challenges in estimating and closing the water and energy budgets of the Earth? What inhibits our understanding of the dynamic relationships between human water use, water fluxes and storages, and the global climate? What are the bottlenecks caused by the lack of global or regional observations? Can we use remote sensing based data and hydrologic models to bridge the gap caused by the dearth of observations for monitoring the water cycle?
  2. Accounting Human Factors in Hydrologic Models: What are the major challenges in realistically simulating the contemporary terrestrial water cycle? What are the primary limitations in the current-generation state-of-the-art hydrologic models? Does the incorporation of human factors in the models help better estimate the available water resources today and reliably project them for the future? What are the relevant spatial and temporal scales for the human impacts to significantly alter water fluxes and storages?
  3. Global Water and Food Sustainability: What will be the hydrologic response to global climate change? Do dry places become even drier? How will the already scarce regional and global water resources fare under increasing human pressure and changing global climate? Will there be enough water to produce food required to feed the escalating population in the upcoming decades?
  4. Groundwater Overexploitation: What is the role of groundwater in contemporary water use and where are the major hotspots of groundwater overexploitation? How long can we keep going if we exploit groundwater at the same rate as we have done in the past? What is the ultimate fate of groundwater pumped from aquifers? Does it ultimately flow to the oceans and increase the rate of sea level rise?
  5. Groundwater and Terrestrial Water Storage (TWS): What is the role of groundwater in modulating TWS variations in different geographic and climatic settings? How can we realistically estimate various TWS components in hydrologic models? What are the mechanisms whereby these TWS components affect various hydrologic fluxes? Does groundwater store play an important role of buffer to reduce moisture stress in dry season in the regions where climate change may result in an even drier dry-season?