[1] A large amount of water is stored in the world's highest and largest plateau, the Tibetan Plateau, in the forms of glaciers, snowpacks, lakes, and rivers. It is vital to understand where these waters come from and whether the supply to these water resources has been experiencing any changes during recent global warming. Here we show the maintenance of water content in the atmosphere over the Tibetan Plateau, the atmospheric circulations and transports of water vapor to this part of the world, and the trend of the water vapor supply. The Tibetan Plateau serves as a role of ''the world water tower'', and its land-ocean-atmosphere interaction provides a profound impact on the global natural and climate environment. The analyses of a half-century time series of atmospheric water vapor, precipitation, and surface temperature indicate that the atmospheric supply to this water tower presents an increasing trend under recent global warming condition.

Surface rain rate can be simply formulated with the sum of moisture and cloud sources/sinks. In this study the moisture sink comprises the local moisture change, moisture convergence (with an imposed vertical velocity), and surface evaporation, whereas the cloud source/sink comprises the local hydrometeor change since the cyclic boundary condition leads to zero hydrometeor convergence. The sources/sinks and their contributions to the surface rain rate are examined based on hourly zonal mean simulation data from a two‐dimensional cloud‐resolving model. The model is forced by the large‐scale vertical velocity, zonal wind, and horizontal advections obtained from Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE). Although variation in the moisture sink largely accounts for much of the variation in the surface rain rate, the cloud source/sink may modify the surface rain rate significantly. The magnitude of the cloud source/sink increases when the zonal mean surface rain rate increases from 0 to 1 mm h−1, and it decreases when the rain rate increases from 1 to 2 mm h−1. The cloud source/sink is further analyzed by breaking it into ice and water hydrometeors. The ice hydrometeors may account for more contributions to the cloud variations than the water hydrometeors, and their growth may lead the surface rain rate by 1–2 hours.

The discontinuity of the latent heat term could occur in the thermodynamic equation in the transition area between the unsaturated and saturated air where the latent heat is released associated with the condensation in the saturated air whereas the latent heat is not released in the unsaturated air. To fix the discontinuity, the condensation probability function ()k (q and qs are specific humidity and saturated specific humidity respectively, k = 9) is introduced into the thermodynamic framework with ()kqs. The generalized moist potential vorticity (GMPV) is thus defined and its tendency equation is derived. The analysis shows that in a frictionless and moist adiabatic flow, the GMPV can be generated in the unsaturated air only and its generation rate is determined by the environmental moisture and its gradient.

Based on International Satellite Cloud Climatology Project (ISCCP) Convection Tracking Database (CTD) data set, a new definition for the Tibetan Convective System (TCS) is introduced, in which the effects of cirrus and cirrostratus are excluded from the TCS over this region. 2032 TCSs are selected to study their seasonal variations in initiation, frequency, spatial distribution, life cycle, cloud physics, precipitation, and dynamic and thermodynamic characteristics. It is found that the number of TCSs varies seasonally, with the maximum in July and minimum in December. The 10%, 8%, 9%, and 73% TCSs are originated from Tibetan shear, vortex, low, and the rest, respectively. TCSs play an important role in the precipitation of the Tibetan Plateau and its adjacent regions. Even in winter, the rainfall of TCS contributes up to 70% of the total precipitation over the central-eastern Tibetan Plateau and 30%-70% over Sichuan basin and upper-middle segment of Yangtze River basin. The seasonal changes of TCSs' cloud properties from ISCCP indicate that the strongest TCSs happen in summer and the weakest in winter, which are consistent with the seasonal variation of TCSs' rainfall observed by TRMM. Besides, TCSs show an asymmetric dynamic and thermodynamic distribution, especially in summer.Recently, the development of newly data sets from meteorological satellite and remote sensing data as well as some advanced detection methods contribute a lot to the knowledge of TCS. For example, following Maddox's idea [1980], some new definitions about TCS are introduced to study the genesis, growth, decay, and precipitation of TCS using satellite data. Based on the temperature of black body (TBB) of Geostationary Meteorological Satellite (GMS), Jiang et al. [1996] and Jiang and Fan [2002] found that two convective centers (i.e., the southeast center and the relatively stronger southwest center) exist over the Tibetan Plateau in summer, and only a small portion of TCSs can move out plateau and influence precipitation over the Yangtze River basin. Using the Polar Satellites IR data in the summers of 1998-2000, Shan et al. [2003 indicated most of TCSs were banded, comma-like, and other irregular types over Tibetan Plateau; only 30 % of them took on circular and ellipse types during their genesis; strong monsoon activity plays a major role in TCSs' formation. Using GMS LIANG ET AL. Key Points: • TCSs' rainfall contributes to up to 70 % of total precipitation over the central-eastern area of the Tibetan Plateau • TCSs play an important role in the rainfall of Tibetan Plateau in summer and also in winter • Some evidences about previous knowledge of the TCS are presented based on a 7 year TRMM and ISCCP satellite observation

No abstract

No abstract

Agro‐climatic classification helps to determine the different features of a region. This climatic classification provides a useful insight for a farmer to grow their crops according to the conditions of their region. This study identifies the shifting of moisture index from average values in different agro‐climatic zones of Pakistan. Unpredictable climate remains dominant over long periods. Observational data of precipitation and evapotranspiration were used to determine the agro‐climatic zone during the period 1951–2010. This study reveals that almost 87% of Pakistan is in extremely arid to semi‐arid zones, a 5% decrease in over the last 30 years (1981–2010). The largest decrease of 8% and increase of 5% were observed in the extremely arid and humid zones, respectively. The semi‐arid zone is more vulnerable to drought, while intensity and severity are greater in the extremely arid region. An agro‐climatic regional analysis identifies 1952, 1969, 2000, 2001 and 2002 as years when the most severe droughts were observed during the study period. The trends of precipitation and temperature were performed at 95% significance level on a monthly, seasonal and annual basis over the entire agro‐climatic zone of Pakistan during 1951–2014. The annual precipitation trends show a significant increase of 0.828 mm year−1 in arid regions, whereas the maximum temperature trends shows a significant increase of 0.014 °C year−1 and 0.018 °C year−1 in extremely arid and humid regions, respectively. The trend of minimum temperature shows an increase over the whole region, which may place pressure on the water demands of crops.

Summer convective systems (CSs) initiated over the Tibetan Plateau identified by the International Satellite Cloud Climatology Project (ISCCP) deep convection database and associated Tropical Rainfall Measuring Mission (TRMM) precipitation for 1998-2001 have been analyzed for their basic characteristics in terms of initiation, distribution, trajectory, development, life cycle, convective intensity, and precipitation. Summer convective systems have a dominant center over the Hengduan Mountain and a secondary center over the Yaluzangbu River Valley. Precipitation associated with these CSs contributes more than 60% of total precipitation over the central-eastern area of the Tibetan Plateau and 30%-40% over the adjacent region to its southeast. The average CS life cycle is about 36 h; 85% of CSs disappear within 60 h of their initiation. About 50% of CSs do not move out of the Tibetan region, with the remainder split into eastwardand southward-moving components. These CSs moving out the Tibetan Plateau are generally larger, have longer life spans, and produce more rainfall than those staying inside the region. Convective system occurrences and associated rainfall present robust diurnal variations. The midafternoon maximum of CS initiation and associated rainfall over the plateau is mainly induced by solar heating linked to the unique Tibetan geography. The delayed afternoon-late night peak of rainfall from CSs propagating out of this region is a combined outcome of multiple mechanisms working together. Results suggest that interactions of summer Tibetan CSs with the orientation of the unique Tibetan geography and the surrounding atmospheric circulations are important for the development, intensification, propagation, and life span of these CSs.