Research Overview

Motivation of SASWE Research Group

The systematic decline of in situ networks for hydrologic measurements (such as rainfall, soil moisture, river discharge) has long been recognized as a crucial limitation to advancing water resources management in medium to large basins, especially those that are already sparsely instrumented. As a collective response, sections of the hydrologic community have recently forged partnerships for the development of space-borne missions for cost-effective, yet global, hydrologic measurements. Examples are the SMAP mission for global mapping of soil moisture conditions, the SWOT mission for surface flow measurement and the GPM mission for global monitoring of rainfall. In about a decade from today, there is no doubt that the scientific community as a whole will become dependent on these space-borne missions for most of its data needs for large-scale water resources management. A new discipline will emerge on global water resources management based on water measuring satellites. The SASWE Research Group recognizes this changing landscape of data availability and the need to harness the potential that space-borne water-measuring missions hold for alleviating problems of water resources management. Resource-poor developing nations in particular are currently ill-equipped to leverage these missions and yet appear the biggest beneficiaries. It is therefore important that leadership is provided to these nations on the path to the most cost-effective use of these proposed missions.

While the benefits from proposed water-measuring satellite missions are conceptually apparent, the hydrologic community needs to exercise caution before rushing to prototype ambitious applications. For example, in the case of GPM, there is an urgent need to first resolve some critical and open hydrologic issues that satellite precipitation products currently pose as a challenge to (overland) user community of hydrologists. Satellite precipitation development has witnessed considerable progress in enhancing predictability of meteorological processes (such as improving hurricane tracking and understanding urban modification of local climate by TRMM). However, it has not kept pace with the emerging needs for realistic characterization of large-scale surface hydrologic processes. A crucial challenge in connection to advancing satellite rainfall-based surface hydrologic prediction is the need to bridge the scale incongruity between overland hydrologic processes that evolve at finer dynamic scales and operational satellite rainfall forcing datasets that are available at coarser scales that are larger by at least an order. Water resources managers need to have a clear understanding of the pros and cons of applying satellite rainfall data for terrestrial hydrologic applications at a given scale if the benefit from GPM is to be maximized. The SASWE Research Group is committed to identifying these ‘pros and cons’ of satellite data usage so that realistic and cost-effective systems can be designed for resource poor nations without any potential misuse for water resources management.

In particular, there are two areas that SASWE Research Group aims to develop a niche for in scientific research: 1) ungauged river basins in the tropics and (2) international river basins (IRBs). IRBs are ubiquitous in the five major continents where a total of 145 countries comprise the drainage areas. These basins account for more than 40% the earth’s inhabitable land mass. A comparison of the global distribution of large-scale flood events with a map of IRBs (see Figure 1, lower two panels) reveals a commonality that is currently overlooked in most water resources and environmental management research. Specifically, for flood-prone nations situated in the downstream end of IRBs, issuing effective flood warnings for decision-support purposes can be particularly difficult under two conditions: (1) when surface measurements of rainfall and other land surface parameters are largely absent due to inadequate in situ infrastructure (that is correlated with availability of financial resources) (Figure 1, compare between upper and lower pair of panels) and (2) when there is no political agreement between the riparian nations lying within the watershed to share real-time rainfall data (Figure 1, compare between lower panels).

It is estimated that there are at least 33 countries forced to cope with a situation where much, if not most, of floodwaters they need to predict are generated beyond their borders (known as ‘transboundary flooding’)This fact makes these “locked” countries highly dependent on real-time rainfall information from outside their borders. Furthermore, many of these downstream IRB nations lack adequate surface weather stations, so that even within their borders there is an absence of real-time rainfall measurements. These combined effects lead to a poor ability to mitigate flood effects due to the absence of an early warning system.

In addition to the above, the SASWE Research Group aims to make fundamental contributions in transforming 20th century Civil Engineering (water resources) practice to one that is more ’21st century’ and more cognizant of the inter-linked connections with the local climate. This is planned through translation of recent SASWE-discovered understanding of human modification of hydroclimatology by large water infrastructures (e.g dams/reservoirs, irrigation projects) to newer Civil Engineering design, operation and management protocols for the new century. Due to the interactions of the atmospheric processes with surface water, understanding and predicting the effect that human-modified, flood-frequency behavior has on sustainable dam design, reservoir operations and water management in impounded basins cannot be achieved by stand-alone hydrologic-hydraulic models as has been historically pursued by the engineering profession. In the United States alone, more than 85% of large dams will be over 50 years old by 2020 thus becoming prone to higher flood risks not just from loss of storage (or lower runoff from drought) but also from a potential change in magnitude of extreme precipitation. Across the globe, more water resources projects will continue to be planned due to increasing water demand from population growth and projected changes in climate. The SASWE Research Group hopes that this line of work will jumpstart the civil engineering profession worldwide to a design approach that is considerably more sustainable and safer than 20th century dam/reservoir building practices.

Figure 1. Spatial dependency between the occurrence of large-scale floods and the geographical location of international river basins (IRBs) shown through two connecting themes: rainfall and lack of economic resources of nations. Top panel: climatologic rainfall map produced with data from the Tropical Rainfall Measuring Mission (TRMM). 2nd panel from bottom: global distribution of floods in 2003 (from the NASA-supported Dartmouth Flood Observatory). 2nd panel from top: World Bank estimate of GDP per capita of nations in 2001 (lighter shaded countries are poorer). Bottom panel: map of IRBs with the darker shaded IRBs projected to be in a state of higher water stress due to lack of cooperative agreement for sharing water resources and data (courtesy of Dr. Aaron Wolf of Oregon State University).

Figure 2. Generalization of the transboundary flood problem faced in International River Basins. The red boundary indicates the river basin’s topographic limit, while the brown lines are political boundaries of riparian nations. With the absence of treaty for real-time data sharing, it is obvious that satellites from space are the only alternative for a nation to acquire basin wide rainfall data and predict in real-time the generated runoff and stream flow (shown in arrows).

The SASWE Research Group aims to provide support to the hydrologic community that will be critical to assure that satellite missions hydrologically as vital as GPM, SWOT and SMAP are kept alive. Because the evolution of global hydrology is one of the most important trends in hydrology in recent decades and is critical to water resources management, the availability of global observations, many of which are only feasible from space, needs to be a key element of this study area. “For all of these reasons, strong and vocal support along with a concerted effort to resolve critical hydrologic challenges posed by water-measuring satellite missions are central to the continued health of an area that is increasingly important to hydrology and the global society”.