Since the 1950s, the Tibetan Plateau has experienced pronounced warming and wetting. However, an overall shift toward wetter conditions does not necessarily mean that drought risk has diminished. On the contrary, against the backdrop of continued warming, compound hot-dry events—characterized by the simultaneous occurrence of high temperatures and drought—have become an increasingly important climate risk across the Plateau. Such extremes can directly affect ecosystems and water resources, accelerate glacier retreat and permafrost degradation, destabilize glaciers and high-mountain geomorphic systems, and potentially increase the risk of secondary hazards such as ice avalanches and landslides. Yet the processes governing the year-to-year variability of these compound hot-dry events remain poorly understood.
A recent study, published in Journal of Geophysical Research: Atmospheres and led by Prof. Tianjun Zhou's research team at the Institute of Atmospheric Physics, Chinese Academy of Sciences, has helped fill this knowledge gap. "We found that the year-to-year swings in these compound hot-dry events are not random—they are largely steered by two major climate modes: ENSO and the Summer North Atlantic Oscillation," says lead author Rongyun Pan, a PhD candidate at the institute. The study shows that these large-scale patterns modulate atmospheric circulation and surface energy balance across the Plateau, driving the alternating hot-dry and cool-wet summers.
The researchers used the High-Resolution Near‐Surface Meteorological Forcing Data set for the Third Pole region (TPMFD), together with the CN05.1 observational dataset and ERA5 reanalysis, to investigate the spatiotemporal characteristics of summertime compound hot-dry events over the Tibetan Plateau since 1979.
The results show that ENSO conditions during the preceding winter exert a pronounced influence on compound hot-dry events over the southwestern Tibetan Plateau in the following summer. During El Niño years, the regional mean number of compound hot-dry days increases by approximately 1.85 days, whereas during La Niña years it decreases by about 1.13 days. In general, stronger ENSO events tend to produce a more pronounced modulation.
The researchers further distinguished between eastern Pacific (EP) and central Pacific (CP) types of ENSO. During EP El Niño years, the number of hot days can increase by more than 7 days in parts of the southwestern Plateau, while the regional mean number of drought days increases by 11.4 days. This enhancement is associated with changes in cloud radiative effects and clear-sky shortwave radiation, which together increase the amount of energy received by the land surface.
In contrast, CP La Niña exerts the strongest suppressing effect on compound hot-dry events. Changes in cloud radiative effects and surface albedo reduce the energy input to the land surface, favoring the persistence of cooler and wetter conditions. On average, the numbers of hot days and drought days decrease by 6.2 days and 8.2 days, respectively.
Meanwhile, local land–atmosphere interactions act as an “amplifier” over the southern Tibetan Plateau endorheic region. As the soil dries, less water is available for evaporation. Consequently, a larger fraction of the available surface energy is converted into sensible heat flux rather than being consumed by evaporation, further warming the near-surface atmosphere. The resulting rise in air temperature, in turn, intensifies surface drying, creating a self-reinforcing hotter–drier feedback.
The Summer North Atlantic Oscillation (SNAO) provides another important source of variability, particularly for compound hot-dry events over the eastern Tibetan Plateau. Through Rossby wave trains propagating eastward along the Eurasian westerly jet, SNAO-related circulation anomalies originating over the North Atlantic can influence atmospheric conditions as far east as the Tibetan Plateau.
The local response over the eastern Plateau, however, exhibits a pronounced north–south contrast. During the positive phase of the SNAO, compound hot-dry events generally become more frequent across the eastern Plateau. In the relatively humid southeastern Tibetan Plateau, reduced precipitation and cloud cover allow more solar radiation to reach the land surface. The resulting increase in surface heating associated with changes in cloud radiative effects therefore plays a dominant role in warming.
By contrast, over the relatively arid northeastern Tibetan Plateau, warming is governed more strongly by changes in downward radiation under clear-sky conditions. In other words, although both regions ultimately experience hotter and drier conditions, the surface energy processes responsible for the warming differ substantially between the southeastern and northeastern Plateau.
"This study bridges the gap between large-scale climate drivers and local surface processes," says Prof. Tianjun Zhou, the corresponding author of the study. "By linking ENSO and SNAO teleconnections with land–atmosphere feedbacks, we now have a more complete physical framework to understand why these compound hot-dry events vary so much from year to year over the Tibetan Plateau."
The findings help explain why unusually “hot and dry” summers can still occur frequently over a region that has undergone long-term warming and wetting. They also provide a physical basis for improving seasonal prediction and risk assessment of compound climate extremes over the Tibetan Plateau by exploiting potentially predictable climate signals such as ENSO and SNAO.
Interannual Variability of Compound Hot‐Dry Events Over the Tibetan Plateau
1-Sep-2026