Abstract. Time series of Penman-Monteith potential evapotranspiration estimates for 101 stations on the Tibetan Plateau and surrounding areas are analyzed in this paper. For the Tibetan Plateau as a whole potential evapotranspiration (PET) has decreased in all seasons. The average annual evapotranspiration rate decreased by 13.1 mm/decade or 2.0% of the annual total. Superimposed on this general decline are fluctuations ranging from app. 600 to 700 mm with above average rates in the 1970s and 1980s. On a regional basis, spatial trend distributions remain stable throughout the year with similar seasonal variations. Decreasing PET rates are more pronounced in winter and spring (80% of all stations) as compared to summer and autumn (58% of all stations). Maximum negative (positive) annual rates were recorded at two stations in the southern Qaidam Basin with −79.5 mm/decade (84.8 mm/decade) even though in general negative rates tend to be noticeably higher than positive rates.Changes in wind speed and to a lesser degree relative humidity were found to be the most important meteorological variables affecting PET trends on the Tibetan Plateau while changes in sunshine duration played an insignificant role. Stable daytime temperatures on the Tibetan Plateau have limited the importance of temperature trends for changes of PET rates. Negative evapotranspiration trends are therefore thought to be linked to a general decrease in intensity of the regional monsoon circulation rather than to reductions in sunshine duration. Reduced PET rates appear to be in contrast to a predicted increased hydrological cycle under global warming scenarios.

The summer day-by-day precipitation data of 97 meteorological stations on the Qinghai-Tibet Plateau from 1961 to 2004 were selected to analyze the temporal-spatial distribution through accumulated variance, correlation analysis, regression analysis, empirical orthogonal function, power spectrum function and spatial analysis tools of GIS. The result showed that summer precipitation occupied a relatively high proportion in the area with less annual precipitation on the Plateau and the correlation between summer precipitation and annual precipitation was strong.

Agriculture and climatic trends in the central Yarlong Tsangpo valley, Tibet The Yarlong Tsangpo valley in southern Tibet is the centre of Tibetan farming. About 75% of the area is cultivated with local barley cultivars with some additional spring and winter wheat. With the exception of the Xigaze basin, cultivation is limited by seasonal flooding to higher ground on terraces, debris fans and small upslope areas in the valley. Generally favourable thermal and solar conditions in the subtropical high-altitude valley at elevations between 3,500-3,900 m are offset by low precipitation and high evapotranspiration rates. Previous temperature-based estimates of evapotranspiration rates underestimate the actual conditions considerably; annual Penman-Monteith evapotranspiration totals are estimated at 1,194 und 1,364 mm for Lhasa and Xigaze. Based on long-term water balance calculations (1954-1990), the seasonal water demand of barley and wheat is estimated at 460-730 mm (580-770 mm) and 530-840 mm (660-920 mm) at Lhasa (and Xigaze, resp.). Mean total plant-available water during the growing season amounted to only 54-59% and 44-49% of the seasonal water demand (wheat and barley, resp.) at Lhasa and Xigaze, resp. and decreased by 12% and 4-8% during that period. Estimated water balance data therefore point to increasingly arid conditions in the region. A shift towards cultivating more drought-tolerant barley cultivars instead of wheat, and raising the effectiveness of irrigation systems are possible counter measures. Zusammenfassung: Das Yarlong Tsangpo-Tal in Südtibet ist das Zentrum des tibetischen Ackerbaus. Lokale Gerstensorten nehmen neben Sommerweizen und Winterweizen ca. 75% der Getreideanbauflächen ein. Mit Ausnahme des Beckens von Xigaze beschränken sommerliche Hochwasser den Anbau überwiegend auf die Nutzung höhergelegener Terrassen, Schwemmfächer und vereinzelter Hanglagen. Den für ein subtropisches Hochtal mit mittleren Höhenlagen von 3.500-3.900 m günstigen thermischen und solaren Bedingungen stehen geringe Niederschläge und hohe Verdunstungsraten gegenüber, die von bisherigen temperaturgestützten Berechnungen der Verdunstung erheblich unterschätzt wurden. Jährliche Penman-Monteith-Evapotranspirationssummen für Lhasa und Xigaze betragen 1.194 und 1.364 mm. Auf der Basis von langjährigen Wasserbilanzberechnungen ergibt sich zwischen 1954 und 1990 eine hohe Schwankungsbreite des saisonalen Wasserbedarfs für Gerste (460-730 mm bzw. 580-770 mm) und Weizen (530-840 mm bzw. 660-920 mm, jeweils in Lhasa und Xigaze). Damit werden in Lhasa im Mittel nur 54-59%, in Xigaze nur 44-49% des saisonalen Wasserbedarfs durch Niederschlag und Bodenwasser gedeckt. Diese Wasserbilanz hat in Lhasa im Beobachtungszeitraum um je 12% und in Xigaze zwischen 4% und 8% (Gerste bzw. Weizen) abgenommen. Die berechneten Wasserbilanzen weisen damit auf eine Verschiebung der Klimaverhältnisse zu arideren Bedingungen hin. Bevorzugter Anbau der trockentoleranteren Gerste anstelle von Weizensorten und eine Instandsetzung der Bewässerungssystem...

In terms of demands of rice farming in the southern China, the information processing system and the yield measurement system that is installed in combine harvester, are designed and completed. Now the systems have been used in demonstration site in the Experiment Base of Shanghai Precision Agriculture. Based on the idea of spatial-oriented, object-oriented, user-oriented, the Farm Geographic Information System for precision farming of rice was developed, which is characterized by intelligence and visualized. The Decision-making Management System is integrated with rice growth model, expert model for rice cultivation. The DGPS, RS, GIS and intelligence sensors and computer technique were adopted in building the artificial intelligence system for measuring grain yield that is installed in combine harvester, so the combine harvester could provide the grain yield distribution map real-timely. The environmental and economic assessment shows that the precision rice farming applied in the demonstration site will benefit the society, economy and ecology greatly.