Investigations on the impact of land-use changes and/or radiative forcing on water availability and the pathways and interactions of the global and regional water cycles

Principal Investigator: Nicole Mölders

Research assistant: Zhao Li

Water availability is an essential need for the welfare of the still increasing population. Therefore, a fundamental knowledge is required on (1) the variability of the water cycle at various scales, and (2) the uncertainty in predicted (future) water availability, especially under the condition of global change. The primary goal of the proposed research project is to examine the impact of different radiative forcing and/or man-made land-use changes on the water cycle and water availability in selected regions and their interaction with the global water cycle to estimate the uncertainty in predicting the water cycle caused by anthropogenic land-use changes and the increase of CO2. Here, it is to be investigated whether land-use changes have the same impact under different radiative forcing conditions with respect to water management purposes. Finally the potential of managing water availability in response to global change is to be exploited by substituting the vegetation-category in the sensitive areas by categories that have opposite hydrological demands to offset the change.

To achieve these aims (1) simulations with a climate system model have to be performed, and (2) tools have to be developed for data analysis. The state-of-the-art Community Climate System Model (CCSM) of the National Center for Atmospheric Research (NCAR), which includes fully interacting component models of the oceans, atmosphere, land, and sea ice, will be used. It is to be run for 30 years (after spin-up) without and with land-use changes in four test regions (basins of the Yukon, Ob, St. Lorenz, Colorado and their contributors), both under three different radiative forcing (1 x CO2, 2 x CO2, 3 x CO2), which makes up 6 simulations in total. These test regions were exemplary chosen because of their differences in hydrologic regimes. Although the Yukon and Ob are both located in the Arctic they differ from wetness, amount of permafrost, the complexity of terrain, and ocean to which they discharge.

Tools were developed to examine the interaction between the slow, medium, and fast components of the water cycle, the global and regional/local scale, the changes of the water cycle under altered radiative forcing and land-use, and the change in frequency of events (e.g., droughts, floods, etc.). They include programs for budgeting (a precipitation recycling model enlarged for consideration of runoff), frequency and similarity analysis, detecting non-linearity, sensitive and affected areas. To evaluate the interaction between the global and regional/local water cycle, the four test regions were defined in form of equal-size boxes over the test basins with the basins in their center. Precipitation, and evapotranspiration within these boxes and in- and outflow of atmospheric water constituents, water vapor, as well as runoff were determined at the boundaries of these boxes. The temporal behavior of these quantities and its change due to the two aspects of global change mentioned above as well as their combination were examined. Moreover, the in- and outflow across the equator and the 60ºN latitude line was determined to estimate and evaluate recent and the change in the inter-hemispheric and mid-latitude-arctic exchange of water. Ratios of the predicted water cycle relevant quantities gained from simulations without and with the anthropogenic changes were calculated to detect the radius of influence of land-use changes. Similarity analysis is performed on various temporal averages determined for each grid point to detect areas of similar/dissimilar behavior under the various radiative forcing and land-use conditions.

Publications:

Acknowledgements: This work is financially supported by the National Science Foundation under Grant No. 0232198. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.