Biosphere-Atmosphere-Hydrology Interactions in Semiarid Environments II
Presiding: C J Watts, Universidad de Sonora; E R Vivoni, New Mexico Institute of Mining and Technology
A34B-01 INVITED 15:35h
Research by the SAHRA Center to Investigate the Effect of Vegetation Change on Water Resources in the Southwestern US
Vegetation change is a common feature of the Southwestern landscape. Over the last several decades this has occurred in the form of shrub invasion of grasslands, expansion of pinyon-juniper, thickening of ponderosa pine forests, and anthropogenic land-use changes. More recently drought related fires and bark beetle infestations are resulting in large-scale vegetation change. Also in the semiarid Southwest, most human settlements, irrigated agriculture, and regional biodiversity are located in riparian corridors. These riparian systems integrate the hydrologic and biogeochemical processes that occur within a basin. Consequently, water resource management decisions may impact river systems not only through changes in streamflow, but also through changes in water quality, the socioeconomic value of the river system, and the structure and diversity of the riparian ecosystem. Recognizing the need for research to address these critically important issues, the NSF Science and Technology Center for Sustainability of semi-Arid hydrology and Riparian Areas (SAHRA) is focusing research which addresses the questions "What are the impacts of vegetation change on the basin-scale water balance?" and "What are the costs and benefits of riparian restoration and preservation?" This talk will overview SAHRA's past and current research into these questions and preview SAHRA's new research initiatives in this area.
http://www.sahra.arizona.edu/
A34B-02 INVITED 15:55h
Integrated modelling and remote sensing approach for sustainable management of water resources in a semi-arid basin in Morocco (SUDMED
In southern Mediterranean regions, water consumption has increased by 60% in the last decades and continues to rise while available water resources are becoming increasingly scarce. This situation has raised public awareness of long-term water resources issues. However, due to a combined shortage of expertise and funding, little has been attempted toward the development of a basin-wide hydro-ecological understanding of its functioning, stresses and the consequent hydrological responses to those stresses. In this context, CESBIO/IRD have conceived in a close connection with Moroccan scientists, managers, decision makers and other stake holders an interdisciplinary research program whose general objectives are: - Understanding of critical hydro-ecological processes at the basin scale and addressing them through an integrated research program by making a full use of historical data and newly developed technology such as remote sensing, GIS, and other ground instruments such as scintillometers, isotopic analysis, numerical modelling and data assimilation. - Providing operational tools to mangers and guidance to decision makers which help to make informed decision where the need for the growth/development and the sustainability of water are balanced. In this presentation, we will first outline the specific objectives of the program. Second, we will provide the initial results, ongoing and future investigations. Finally, the issue of transposing the results obtained in Morocco to other semi-arid regions of the world will be discussed.
A34B-03 16:15h
Regional climatic impact of land use change in Southwest Australia
Southwest Australia is a site of drastic land use change, with an estimated 13 million hectares of native vegetation been removed for agricultural purposes. A 750 km rabbit proof fence marks the boundary between the croplands along the Southwest coast and the native vegetation in the continental interior. Due to the high contrast in albedo between the two land use types, the boundary separating these areas is a prominent feature in the satellite images for this region. A 20 precent decrease in rainfall has been observed in the agricultural region; satellite data analysis shows differences in cloud formation and development between the native vegetation and agricultural areas. The remotely sensed Clouds and Earth's Radiant Energy System (CERES) data is used to examine the seasonal variations in the clear sky radiative components of surface energy budget over agricultural and native vegetation areas. The net shortwave flux at the surface is consistently higher throughout the year over native vegetation areas compared to agricultural areas. The maximum difference in the net shortwave flux of approximately 150 Wm-2 occurs during the months of December-January when the agricultural areas are bare after harvest. The difference in net shortwave between the two land use types decreases steadily until August, the peak of the growing season, reaching an average value of approximately 25 Wm-2, after which it remains relatively constant until November. The net longwave flux at the surface is consistently lower over the agricultural areas throughout most of the year except during the months of September-November, when it is approximately the same over both land use types. The maximum difference in net longwave flux of 20Wm-2 occurs during the month of February, with a gradual decrease until September. The differences in radiative components of the surface energy budget, along with varied transpirational characteristics of the vegetation, are responsible for observed differences in cloud formation between the two land use types. Other potential regional climatic impacts, including the alteration of regional circulation patterns, will be discussed.
A34B-04 16:30h
Water use in an Introduced Buffel Grass (Cenchurs Ciliaris) Savanna in an Arid Region.
Buffel grasslands have been a management strategy introduced in Sonoran Desert habitats to reverse degraded productivity in rangelands. Initial scrape of native vegetation but trees results in a savanna type of habitat. We followed evapotranspiration at a site using an eddy covariance approach and water use on individual species. Seasonal pulses of rainfall and total water use were found and compared to known estimates of similar habitats in other arid and semiarid regions. Previous studies of ET on native vegetation close to our study site allowed us to compare changes in the water use of natural and managed vegetation cover under similar habitat conditions.