Precipitation In Central Asia Research Articles

The Interdecadal Weakening of the Relationship Between Indian Ocean Sea Surface Temperature and Summer Precipitation in Central Asia

AbstractThe close relationship between the Indian Ocean Basin mode (IOBM) and summer precipitation in Central Asia (CA) has been documented in several studies. Nonetheless, this relationship has weakened since the 1990s and varies with the Atlantic Multi‐decadal Oscillation (AMO) phase transition. During the cold phase of the AMO (1970–1998), precipitation in CA was significantly positively correlated with the IOBM. Conversely, during the warm phase of the AMO (1999–2019), this correlation became insignificant. The decrease in the interannual variation in the IOBM resulted in the weakening of the atmospheric heat source variation over the North Indian continent and the south‐north movement of the subtropical westerly jet (SWJ). Along with the southerly SWJ, the IOBM exhibited only a weak positive correlation with precipitation in southern CA after the 1990s. This remarkable contrast in the impact of IOBM during different phases of the AMO offers intriguing possibilities for improving climate prediction in CA.

Increased population exposures to extreme precipitation in Central Asia under 1.5℃ and 2℃ global warming scenarios

The increase in extreme precipitation (EP) may pose a serious threat to the health and safety of population in arid and semi-arid regions. The current research on the impact of EP on population in Central Asia (CA) is insufficient and there is an urgent need for a comprehensive assessment. Hence, we opted for precipitation and temperature data under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5) from ten Global Climate Models (GCMs), which were obtained from the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP-CMIP6). Simultaneously, integrating population data in 2020 and 2050 (SSP2 and SSP5), we investigated the future changes in EP and population exposure in CA under 1.5°C and 2°C global warming scenarios (GWSs). Our analysis indicates that EP in CA is projected to increase with global warming. Under the SSP5-8.5, the maximum daily precipitation (Rx1day) exhibits an average response rate to global warming of 3.58 %/K (1.99 %/K – 4.06 %/K). With rising temperatures, an increasing number of areas and populations in CA will be impacted by EP, especially in the Fergana valley. Approximately 25% of the population (land area) in CA is exposed to Rx1day with increases of more than 8.31% (9.32%) under 1.5°C GWS and 14.18% (13.25%) under 2°C GWS. Controlling temperature rise can be effective in reducing population exposures to EP. For instance, limiting the temperature increase to 1.5°C instead of 2°C results in a 2.79% (1.75%–4.59%) reduction in population exposure to Rx1day. Finally, we found that climate change serves as the predominant factor influencing the population exposure to EP, while the role of population redistribution, although relatively minor, should not be disregarded. Particularly for prolonged drought, the role of population redistribution manifests negatively.

The Interdecadal Pacific Oscillation is responsible for the linkage of decadal changes in precipitation and moisture in arid central Asia and the humid Asian monsoon region during the last millennium

Abstract. Reconstruction and observational studies imply a potential linkage of moisture and precipitation change in arid central Asia and monsoonal East Asia, in which the evolution of moisture and precipitation in central Asia is out of phase with that in northern China but in phase with that in southern China. In order to ascertain whether there is a robust linkage between the changes in climate in Asian arid regions and monsoon regions and to elucidate the underlying dynamic mechanisms, we analyzed the Last Millennium Reanalysis dataset and outputs from the Community Earth System Model Last Millennium Ensemble (CESM-LME). The results indicate a significant decadal linkage between precipitation changes in central Asia's arid region and the Asian monsoon region during the last millennium, which is primarily driven by the Interdecadal Pacific Oscillation (IPO). In spring, the positive IPO could enhance westerlies over the Mediterranean Sea and to its east, which could transport more water vapor and cause increased precipitation over central Asia. In summer, the positive IPO is accompanied by a weakened Asian monsoon and southward Asian subtropical westerly jet, which can lead to increased (decreased) summer precipitation over southern China (over northern China and South Asia). The IPO plays a dominant role in connecting the decadal variations in precipitation between arid central Asia and monsoonal Asia by modulating the precipitation of their respective major rainy seasons. Model results suggest that this decadal linkage stems entirely from the internal variability present in the CESM-LME control and all single-forcing simulations. Changes in external forcing factors do not alter this inherent linkage caused by the IPO. Moreover, based on analyses of the aridity index and soil moisture content, this relationship of precipitation variation also causes a similar decadal linkage of moisture changes in central Asia and monsoonal Asia. The differences in the multi-centennial-scale moisture and precipitation variations in the Asian arid region and the monsoon region between the Medieval Climate Anomaly and Little Ice Age are also likely caused by IPO-like sea surface temperature anomalies.

Dominant modes and mechanisms of the interannual variability of atmospheric water vapor content during winter over Central Asia

Atmospheric water vapor content (WVC)—a key component of the water cycle—plays a crucial role as an indicator of precipitation changes and directly influences precipitation in the arid areas of Central Asia. These areas are extremely sensitive to global climate change because of their dry climates and fragile water resource systems, especially during winter. This study analyzes the main interannual variation patterns of the atmospheric WVC during winter over Central Asia and reveals the possible physical mechanism behind the changes in the dominant modes (EOF1 and EOF2) of water vapor. The results show that EOF1 (49.4%)—responsible for the interannual variation of the winter atmospheric WVC in Central Asia—has a uniform monopole mode, while EOF2 (23.7%) shows a reverse north–south dipole distribution (with the boundary being at approximately 44° N). The negative geopotential height anomaly over the high latitudes of Europe and the positive geopotential height anomaly over Central Asia are the major impact factors of EOF1, whereas Central Asia has a prevalence of westerly airflow during winter. By influencing the geopotential height anomaly in Central Asia, the winter Niño 3.4 index intensifies the convergence of Atlantic Ocean moisture with tropical Indian Ocean moisture and their eastward transport. In contrast, EOF2 is mainly affected by the positive geopotential height anomaly over the high latitudes of Europe and the negative geopotential height anomaly over the middle latitudes of this region. In particular, the negative anomaly center of the geopotential height on the eastern side of Central Asia extends westward into Central Asia, resulting in reverse moisture transport by westerly and easterly airflows in the southern and northern parts of Central Asia, respectively. This anomaly is correlated with the formation of anomalous cyclonic circulation over North Africa and Europe because of the negative phase of the Arctic Oscillation, leading to prevailing southerly winds in the south of Central Asia, which correspond to abnormal vertical upward movement; however, the situation in the northern part of Central Asia is the opposite. Therefore, the distribution of winter precipitation in Central Asia shows the following pattern: more in the south and less in the north. This study provides scientific and technological support for the formation of research mechanisms and the prediction of winter precipitation in Central Asia.

Multi-Temporal Variabilities of Extreme Precipitation over Central Asia and Associated Planetary-Scale Climate Modes

Arid- and semi-arid Central Asia is particularly sensitive to climate change. The changes in extreme precipitation in Central Asia stemming from climate warming are the subject of intense debate within the scientific community. This study employed a Morlet wavelet analysis to examine the annual occurrence number of extreme precipitation in Central Asia from May to September during the period of 1951–2005. Their modulating planetary-scale climate modes were identified by using linear regression analysis. Two major scales of the temporal variability were derived: 2–3.9 years and 4–6 years. The dominant variability was a 2–3.9-year scale and was associated with the negative phase of the Polar/Eurasia (POL) pattern. The 4–6-year scale provided a secondary contribution and was closely linked to the negative phase of the North Atlantic Oscillation (NAO). These planetary climate modes acted as precursors of extreme precipitation over Central Asia. The negative phase of POL directly contributed to a negative height anomaly over Central Asia, which was intimately related to extreme precipitation. In contrast, the negative NAO phase possibly manifested as a Rossby wave source, which was subsequently exported to Central Asia through a negative–positive–negative Rossby wave train.

Impact of North Indian Atmospheric Diabatic Heating on Summer Precipitation in Central Asia

Abstract The impact of North Indian atmospheric diabatic heating variation on summer rainfall over Central Asia (CA) at an interannual scale during 1960–2019 was investigated from thermal adaptation and water vapor transportation perspective. The results showed that more precipitation in southeastern CA is associated with the southward subtropical westerly jet (SWJ), caused by the ascending motion and weakened water vapor output on the south side. When the SWJ moves southward, the high-level water vapor transportation on the south side changes from outward (−1.9 × 106 kg s−1) to inward (0.6 × 106 kg s−1), and the positive anomalous relative vorticity advections by the basic westerly winds produce ascending anomalies over southeastern CA. The position change in the SWJ was mainly related to atmospheric diabatic heating over northern India (NI). The thermal vorticity adaptation caused by a weakened heating rate over NI leads to an anomalous upper-level cyclone over southeastern CA, and the associated cold temperature advection eventually cools the upper troposphere of southeastern CA and reduces the temperature gradient at mid-to-high latitudes, leading to the southward SWJ. Thermal adaptation of the circulation and temperature anomaly over southeastern CA to the NI thermal forcing were also verified by numerical experiments. Both the abnormal ascending motions and the weakened outward water vapor associated with the southward SWJ, caused by the weakened heating rate over NI, lead to more summer rainfall in southeastern CA. The changes in diabatic heating over NI are closely related to Indian Ocean SST. When the Indian Ocean SST is warmer, the south Asian summer monsoon weakens, causing less precipitation and, thus, a weakened heating rate over NI. Significance Statement This study established that the northern Indian atmospheric diabatic heating anomalies associated with Indian Ocean SST variation play an important role in influencing precipitation in central Asia (CA). The weakening of the atmospheric diabatic heating over the NI would not only cause an abnormal cyclone and cooling over southern CA through thermal adaptation but also lead to southward subtropical westerly jet (SWJ), ascending motions, and decreased outward water vapor on the south side in southeastern CA, eventually resulting in more precipitation in southeastern CA. The results emphasize the influence of tropical SST and atmospheric heat sources on midlatitude climate and are important for understanding summer precipitation change in southeastern CA.

Anthropogenic influence on extreme temperature and precipitation in Central Asia

We investigate the contribution of anthropogenic forcing to the extreme temperature and precipitation events in Central Asia (CA) during the last 60 years. We bias-adjust and downscale two Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) ensemble outputs, with natural (labelled as hist-nat, driven only by solar and volcanic forcing) and natural plus anthropogenic forcing (labelled as hist, driven by all-forcings), to 0.25^{circ } times 0.25 ^{circ } spatial resolution. Each ensemble contains six models from ISIMIP, based on the Coupled Model Inter-comparison Project phase 6 (CMIP6). The presented downscaling methodology is necessary to create a reliable climate state for regional climate impact studies. Our analysis shows a higher risk of extreme heat events (factor 4 in signal-to-noise ratio) over large parts of CA due to anthropogenic influence. Furthermore, a higher likelihood of extreme precipitation over CA, especially over Kyrgyzstan and Tajikistan, can be attributed to anthropogenic forcing (over 100% changes in intensity and 20% in frequency). Given that these regions show a high risk of rainfall-triggered landslides and floods during historical times, we report that human-induced climate warming can contribute to extreme precipitation events over vulnerable areas of CA. Our high-resolution data set can be used in impact studies focusing on the attribution of extreme events in CA and is freely available to the scientific community.

Spatiotemporal variability in extreme precipitation and associated large-scale climate mechanisms in Central Asia from 1950 to 2019

Increased sea surface temperature, evaporation, air temperature, and moisture holding capacity associated with climate change may the enhance transport of moisture to Central Asia (CA), resulting in increased extreme precipitation events (EPEs). Changes in EPEs may affect the socioeconomic and ecological environment in typical arid and semi-arid regions of CA. Therefore, based on meteorological station data and four reanalyzed precipitation datasets, we used the Taylor diagram, Geo-Detector method, and other methods to examine 10 EPE indices in CA from 1950 to 2019, analyzed their spatial-temporal trends, and quantified the influence of large-scale climate factors on EPEs. The results showed that GSWP3_W5E5 was the optimal option with better performance in terms of monthly and annual precipitation in CA. Overall, EPEs in CA showed an increasing trend, but an abrupt point was found in 1986, when very wet day precipitation (R95p) increased from 36.64 to 47.84 mm; the increasing rate also changed from 0.8 to 5.06 mm/10a. The changes in the Northern Hemisphere Subtropical High Intensity Index (NSI), NINO B Area Sea Surface Temperature Anomaly Index (NINOB), Asian Zonal Circulation Index, and Atlantic Multidecadal Oscillation Index are the main reasons for the increase in EPEs; the NSI and NINOB had the largest contributions to EPEs, with at 44.32 % and 43.80 %, respectively. Additionally, two-factor interactions had a more significant influence. Further analysis revealed that the abnormal warming of sea surface temperature and others led to the strengthen of water vapor transport in CA caused by a series of cyclones and anticyclonic anomalies in the westerly circulation zone, leading to the increase of EPEs. The results obtained in this study can contribute to a more comprehensive understanding of the changes in EPEs and provide a reference for water resource management and disaster prevention in CA.

Impact of the uplift of the Central Asian Orogenic Belt and NE Tibetan Plateau on the East Asian climate since the late Miocene

The uplift of the Central Asian Orogenic Belt (CAOB) and the northeastern (NE) Tibetan Plateau has exerted an important effect on the evolution of the East Asian climate since the late Miocene. However, previous modeling studies were generally based on modern boundary conditions, a direct comparison between the impacts of the uplift of the CAOB and NE Tibetan Plateau was still absent, and the climatic effects of the uplift of these mountains since the late Miocene remain ambiguous. Here, we use the Community Atmosphere Model version 4 (CAM4) with a high horizontal resolution (∼0.63° × 0.47°) combined with late Miocene boundary conditions to investigate the effects of the CAOB and NE Tibetan Plateau uplift on the East Asian climate since the late Miocene. The results indicate that the combined uplift of these landmasses increased the annual precipitation in the uplifted regions and eastern Asia, decreased the annual precipitation in central Asia, strengthened summer monsoon winds over northern East Asia, weakened winter monsoon winds over southern East Asia, and strengthened summer and winter high tropospheric westerly wind at northern high latitudes. Of the two uplifting landmasses, the uplift of the CAOB increased the summer precipitation and strengthened the summer high tropospheric westerly wind at higher latitudes and had a greater impact on the changes in winter monsoon winds and winter high tropospheric westerly wind. By comparison, the uplift of the NE Tibetan Plateau was also important in some aspects, such as the increased annual precipitation in eastern Asia. These results emphasized the important climate effects of the CAOB and NE Tibetan Plateau on the East Asian climate and improved our understanding of the dynamic link between orogenic evolution and paleoclimatic change since the late Miocene.

Historical and projected relationships between the Tibetan Plateau summer monsoon and precipitation in Central Asia based on multi-CMIP6 models

Based on the historical and SSP1–2.6, SSP2–4.5 and SSP5–8.5 experiments from20 Coupled Model Inter-comparison Project phase 6 (CMIP6) models, the historical and projected relationships between the Tibetan Plateau summer monsoon (TPSM) and precipitation in Central Asia (CA) are investigated. The historical experiments show that the CMIP6 models have large uncertainties in simulating the relationships between the TPSM and the Central Asian precipitation and their corresponding dynamic processes. 60% (12) of the CMIP6 models can simulate the close positive correlation between the TPSM and the precipitation in the key region (37°-45°N, 65°-85°E) of CA, but only 8 of them can capture the dynamic processes linked the TPSM and the precipitation in CA during 1971–2010. So we select the 8 models out of the 20 based on their skills in capturing the dynamical processes as observed. Regression analysis shows that the 8 selected models will still simulate the positive correlation between the TPSM and the precipitation in CA and capture their linked dynamic progresses during the second half of 21st century (2050–2099), but with the rising of emission scenarios, the significant area of correlations will gradually shrink. During 2050–2099, 75% of the 8 selected models suggest the TPSM will strengthen, especially in northern monsoon regions, corresponding to significant increase of summer precipitation in the key region (37°–45°N, 65°–85°E) of CA in SSP1–2.6 and SSP2–4.5 experiments. In SSP5–8.5 experiment, 6 out of the 8 selected models also indicate the TPSM will strengthen in the northern monsoon region, corresponding to significant increase of precipitation in most of key region and decrease in eastern key region.

Performance of Seven Gridded Precipitation Products over Arid Central Asia and Subregions

The evaluation of gridded precipitation products is important for the region where meteorological stations are scarce. To find out the applicable gridded precipitation products in arid Central Asia (ACA) for better follow-up research, this paper evaluated the accuracy of five long-term gridded precipitation products (GPCC, CRU, MERRA-2, ERA5-Land, and PREC/L) and two short-term products (PERSIANN-CDR and GPM IMERG) on different time scales for the whole ACA and two subregions, Central Asia (CA) and Xinjiang of China (XJ). Seven evaluation indices were used to evaluate the consistency between the seven gridded precipitation products and observations at 328 meteorological stations for 40 years from 1980 to 2019. The main findings were as follows: (1) Each product can correctly reflect the trend of decreasing annual precipitation in CA and increasing annual precipitation in XJ, except for ERA5-Land. (2) GPCC captured extreme events by 75.9% for heavy rainfall and 67.9% for drought events, and GPM IMERG outperformed PERSIANN-CDR with a capture probability of 61% for heavy rainfall and 50% for drought events. (3) Annually, except for GPCC and CRU without significant deviations (BIAS < 2%), ERA5-Land, GPM IMERG, and PERSIANN-CDR generally overestimated precipitation (20% < BIAS < 60%). MERRA-2 and PREC/L underestimated precipitation, with approximately −5% for PREC/L and −20% for MERRA-2. (4) Seasonally, GPCC outperformed the other four long-term products in all seasons with the lowest BIAS (<0.93%), and GPM IMERG (BIAS < 30.88%) outperformed PERSIANN-CDR. (5) Monthly, the areas with large deviations (BIAS > 60%) for the seven products were near the Tianshan Mountains; comparatively, they performed better in CA than in XJ, with BIAS approximately 20% for CA and 40% for XJ. Despite regional differences, GPCC performed the best across the five long-term products overall, followed by CRU, MERRA-2, PREC/L, and ERA5-Land. For the two short-term products, GPM IMERG outperformed PERSIANN-CDR.

Distinct effects of Tibetan Plateau growth and global cooling on the eastern and central Asian climates during the Cenozoic

The evolution of the climate in eastern and central Asia during the Cenozoic was affected by regional paleogeographic developments and global climate change. Previous studies have mainly investigated the effects of Tibetan Plateau (TP) growth and global cooling for specific time periods. However, the respective contributions of these two factors over time are still poorly understood. In this study, we comprehensively compared the effects of TP growth and secular climate change by integrating existing paleobotanical records and model results across a total of 67 experiments. Our results demonstrate that the effects of TP growth and global cooling on the eastern and central Asian climates differed. During the early Eocene, high atmospheric CO2 concentrations contributed greatly to the relatively wet conditions in eastern and central Asia. Subsequent global cooling tended to cause long-term aridification in eastern Asia. By comparison, TP growth was the key factor for the increasing precipitation in eastern Asia and the decreasing precipitation in central Asia between the late Oligocene and the early Miocene. High atmospheric CO2 concentrations contributed to the increased wetness in eastern Asia in the geological past, and this fact has far-reaching implications for future wetter conditions in this region under anthropogenic forcing.

Precipitation reconstruction since the last deglacial based on the stable carbon isotopic composition of a loess section in western Central Asia

The topography of the Tianshan Mountains and the Pamir Plateau strongly shapes the seasonality of precipitation in Central Asia (CA): cold-season (October-April) precipitation dominates western CA and warm-season (May-September) precipitation dominates eastern CA. The precipitation/moisture patterns between western and eastern CA are completely opposite at seasonal, decadal and centennial scale. However, the pattern contrasts for millennial or longer time scales remain unknown. In this study, we investigated the precipitation variations in western CA, as recorded in a 6.5-m loess section in southern Kazakhstan, which has accumulated since ~14.4 ka. According to the robust relationship between the surface soil organic matter δ13C and the climatic parameters, the δ13C signature is here considered as a precipitation proxy. The record reveals an overall decreasing precipitation before ~6.0 ka followed by an increasing trend afterward, being consistent with the previously reported precipitation records in western CA. The late-deglaciation precipitation in western CA is in phase with that in eastern CA at millennial scales, which are both driven by the North Atlantic Oscillation (NAO) and the Siberian High.

Effect of Nitrogen Application on the Sensitivity of Desert Shrub Community Productivity to Precipitation in Central Asia.

Precipitation variability and nitrogen (N) deposition caused by anthropogenic activities could profoundly impact ecosystem productivity and carbon cycling. In desert ecosystems, vegetation is sensitive to changes in precipitation and N deposition. However, the impacts of large changes in precipitation, especially with a concurrent increase in N content, on plant community remain unclear. In this study, we carried out experiments to monitor the impacts of five precipitation levels and two N levels on the plant community function and composition from the Junggar desert in Central Asia during the period 2018–2019. Our results showed that: (1) Aboveground net primary production (ANPP) significantly increased with increasing precipitation, it followed a positive linear model under normal precipitation range, and nonlinear mode under extreme precipitation events; (2) N application led to an increase in ANPP, but did not significantly improve the sensitivity of ANPP to precipitation change; (3) Changes in N content and precipitation, and their impacts on ANPP were mainly driven by plant density. These results provide a theoretical basis for predict the future dynamics of terrestrial vegetation more accurately under climate change and increasing nitrogen deposition.

Interannual Variation and Prediction of Wintertime Precipitation in Central Asia

Abstract In this study, the interannual variations of winter precipitation over central Asia (CA) are investigated over the period 1948–2018 using both observational analysis and a linear baroclinic model (LBM). The focus is on the characteristics and factors of the leading empirical orthogonal function mode (EOF1) of winter precipitation over CA. The results show that the key circulation anomalies associated with the positive phase of EOF1 feature a tripole pattern that is responsible for transporting moisture from the subtropical North Atlantic region to CA. An examination of the lower boundary conditions indicates that anomalous North Atlantic sea surface temperature (SST), Kara Sea ice in the preceding autumn, and simultaneous snow cover in central Asia can promote large-scale atmospheric waves that contribute to the EOF1-related anomalous tripole pattern. This result is verified by an analysis of the apparent heat source (Q1) in the atmosphere and the LBM experiments. Linear regression (LR) models were constructed using the precursors revealed by the above observational analyses to perform hindcasts for EOF1 over the period 1950–2018. The North Atlantic SST and the Kara Sea ice in the preceding autumn are shown to be effective predictors in the LR model that can capture the variation in EOF1 during this period. The seasonal forecasts of winter precipitation over CA for the 2011–18 period based on the LR models outperform those of the Climate Forecast System version 2 (CFSv2) over central and northern CA.

Contribution of precipitation and temperature to multiscale drought variations over Asia: Dependence on the time scale

AbstractDrought variations are determined by precipitation and temperature changes. The present study examines the relative contributions of precipitation and temperature to temporal variations of short‐term, medium‐term and long‐term droughts over Asia. This is accomplished by comparing (a) the variations of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) that extend over 3, 9 and 24 months (i.e., short‐term, medium‐term and long‐term droughts, respectively) and (b) the strength of the relationship of SPEI to precipitation and temperature. Both precipitation and temperature contribute to variations of the north–south dipole pattern of short‐term and medium‐term droughts with a relatively larger contribution from temperature. The contribution of precipitation and temperature to the variations of long‐term drought depends upon the spatial pattern. The variation of the north–south dipole pattern of long‐term drought is mainly contributed by the temperature trend with additional contribution of precipitation in eastern and southwestern Asia. The variation of the southwest–northeast tripole pattern of long‐term drought is mainly contributed by precipitation in central Asia and has a comparable contribution of precipitation and temperature in southern and eastern Asia. The tripole pattern and dipole pattern of long‐term drought have a closer relation to the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), respectively. The PDO effect on long‐term drought variation is mainly through modulating precipitation.

Lagrangian Analysis of Moisture Sources of Precipitation in the Tianshan Mountains, Central Asia

AbstractThe moisture sources of precipitation in the Tianshan Mountains, one of the regions with the highest precipitation in Central Asia during 1979–2017 are comprehensively and quantitatively summarized by using a Lagrangian moisture source detection technique. Continental sources provide about 93.2% of the moisture for precipitation in the Tianshan Mountain, while moisture directly from the ocean is very limited, averaging only 6.8%. Central Asia plays a dominant role in providing moisture for all sub‐regions of the Tianshan Mountains. For the Western Tianshan, moisture from April to October comes mainly from Central Asia (41.4%), while moisture from November to March is derived primarily from Western Asia (45.7%). Nearly 13.0% of moisture to precipitation for Eastern Tianshan in summer originates from East and South Asia, and the Siberia region. There is a significant decreasing trend in the moisture contribution of local evaporation and Central Asia in the Eastern Tianshan during winter. The contribution of moisture from Europe to summer precipitation in the Central and Eastern Tianshan and the contribution of the North Atlantic Ocean to summer precipitation in the Northern, Central, and Eastern Tianshan also exhibit a decreasing trend. The largest increase in moisture in Western Tianshan stems from West Asia during extreme winter precipitation months. Europe is also an important contributor to extreme precipitation in the Northern Tianshan. The moisture from East and South Asia and Siberia during extreme precipitation months in both winter and summer is significantly enhanced in the Eastern Tianshan.

Influence of Large‐Scale Atmospheric Dynamics on Precipitation Seasonality of the Tibetan Plateau and Central Asia in Cold and Warm Climates During the Late Cenozoic

AbstractThe hydroclimate of the Tibetan Plateau (TP) and Central Asia (CA) plays a crucial role in sustaining surface water reservoirs and thus water resources in the respective regions. In this study, we investigate the changes in Asian hydroclimate and its driving forces during specific time intervals in the last 3 Ma. We conduct high‐resolution (∼0.75° per grid cell) general circulation model ECHAM‐5 experiments with boundary conditions for the mid‐Pliocene (∼3 Ma), the Last Glacial Maximum (LGM; ∼21 ka), the mid‐Holocene (∼6 ka), and the pre‐industrial. Results suggest that seasonally relatively high precipitation rates (>1 mm day−1) were longer in the mid‐Pliocene and shorter in the LGM, relative to the pre‐industrial. We calculate different monsoon indices to detect changes in the intensity, strength and duration of the East Asian summer monsoon (EASM), South Asian summer monsoon (SASM), and the Indian summer monsoon (ISM), and construct climatologies of mid‐latitude high‐level westerly jet (WJ) stream occurrences based on the ECHAM5 wind fields. Our results suggest that in warm periods (e.g., mid‐Pliocene or interglacial), the WJ migrates northward earlier in the year (April) and reaches higher latitudes than in the pre‐industrial, resulting in a wetter TP and CA. During cooler periods (e.g., LGM or glacial), the WJ migrates northward later in the year (June) and remains over lower latitudes, resulting in a drier TP and CA. Increased/decreased local precipitation in TP and CA for the mid‐Pliocene/LGM experiments correlates strongly with (a) intensity, strength and duration of the EASM, SASM, and the ISM and (b) WJ latitudinal position.

Future changes in extreme precipitation in central Asia with 1.5–4°C global warming based on Coupled Model Intercomparison Project Phase 6 simulations

AbstractQuantifying future precipitation changes in central Asia (CA), one of the largest semiarid‐to‐arid regions in the world, is increasingly attracting attention. Extreme precipitation changes in CA have been studied based on global climate models (GCMs) in the Coupled Model Intercomparison Project (CMIP). However, quantitative information regarding projected changes in extreme precipitation in CA under the 1.5–4°C global warming scenario is lacking; the potential advantages of the latest‐generation GCMs (i.e., CMIP6) in characterizing precipitation in CA have not been investigated. Thus, in this study, we evaluated the models' overall performance in reproducing the spatiotemporal pattern of four extreme precipitation indices and further performed an observationally constrained projection of changes in extreme precipitation indices for 1.5–4°C global warming based on a weighted multimodel ensemble. Regarding homologous models, CMIP6 models exhibited limited improvement relative to their earlier versions in CMIP5. We project that extreme precipitation indices in CA will increase approximately linearly as global warming increases, except for the consecutive dry days (CDD) index. The changes in precipitation intensity and accumulation exhibit robust consistency between models, whereas the signal of CDD changes is masked by the noise produced by intermodel uncertainties. The changes in the average annual accumulated and maximum 1‐day precipitation relative to the reference period (1981–2010) in CA are 12.0 and 14.2% at 3°C global warming (similar to late‐century warming projected based on current mitigation policies), respectively. Moreover, we demonstrate the advantage of the weighted scheme over the traditional unweighted scheme for multimodel ensemble projection.

Periodic decadal swings in dry/wet conditions over Central Asia

Periodic variability in the hydro-climatic system has important implications not only for climate prediction but also for planning and managing water resources. Here we identify periodic decadal variability of dry/wet conditions in Central Asia (CA) since the mid-20th century, which are tied to the Pacific quasi-decadal oscillation (PQDO) with a period of 8–16 years (r = 0.87). The periodically varying forcing in the Pacific modulates zonal winds and moisture transport and profoundly affects the precipitation on the decadal time scale. The PQDO-related equatorial central Pacific warming significantly heats the overlying troposphere, increasing the meridional temperature/geopotential gradients in the subtropics. As a result, the strengthened westerly jet in CA transports more water vapor from the North Atlantic and increases local precipitation. The plateau to the east further amplifies the increased precipitation in eastern CA through orographic influence on the convection and large-scale circulation. The atmospheric model forced by the PQDO signal reproduces an overall consistent mechanism with the observation, indicating a robust synchronization of the Central Asian hydro-climatic system to the PQDO. The newly discovered oscillatory feature in this study may advance the predictability of Central Asian precipitation on the decadal time scale, which promotes the mitigation and prevention of natural disasters like droughts and wildfires.