Impact of Land Use Change on the Local Climate over the Tibetan Plateau

Observational data show that the remotely sensed leaf area index (LAI) has a significant downward trend over the east Tibetan Plateau (TP), while a warming trend is found in the same area. Further analysis indicates that this warming trend mainly results from the nighttime warming. The Single-Column Atmosphere Model (SCAM) version 3.1 developed by the National Center for Atmospheric Research is used to investigate the role of land use change in the TP local climate system and isolate the contribution of land use change to the warming. Two sets of SCAM simulations were performed at the Xinghai station that is located near the center of the TP Sanjiang (three rivers) Nature Reserve where the downward LAI trend is largest. These simulations were forced with the high and low LAIs. The modeling results indicate that, when the LAI changes from high to low, the daytime temperature has a slight decrease, while the nighttime temperature increases significantly, which is consistent with the observations. The modeling results further show that the lower surface roughness length plays a significant role in affecting the nighttime temperature increase. 1. Introduction It has become apparent that climate change over high-elevation regions is occurring at a faster rate than over low-elevation regions [1]. This high-elevation rate of change often generates stronger disturbances within the climate system than low-elevation changes [2]. The Tibetan Plateau (TP) is an immense upland area ( ), with an average elevation greater than 5,000？m. Over the TP, 46% of the forest cover and 50% of the grassland have been converted to farmland, urban areas, or desert during the last century (X. Liu, personal communication). The TP is the source of snowmelt runoff, supplying water resources to users in China and surrounding areas. The mechanisms influencing the observed rapid climate change and their impacts at this high-elevation region are not well understood. In order to reduce these types of uncertainties and provide society with more reliable projections of future outcomes, detection and analysis of these processes need to be determined. Many researchers have shown that land use and land cover change has remarkab interacts with climate systems [3, 4]. A statistical analysis of the southern half of the Central Valley was performed by Christy et al. [5] using high-quality temperature observations for the San Joaquin Valley in California, where land use has changed dramatically since the presettlement (circa 1860s), due to extensive agricultural expansion. Their study indicated that