Changes In Summer Precipitation Research Articles

High‐resolution dynamically downscaled projections of precipitation in the mid and late 21st century over North America

AbstractThis study performs high‐spatial‐resolution (12 km) Weather Research and Forecasting (WRF) simulations over a very large domain (7200 km × 6180 km, covering much of North America) to explore changes in mean and extreme precipitation in the mid and late 21st century under Representative Concentration Pathways 4.5 (RCP 4.5) and 8.5 (RCP 8.5). We evaluate WRF model performance for a historical simulation and future projections, applying the Community Climate System Model version 4 (CCSM4) as initial and boundary conditions with and without a bias correction. WRF simulations using boundary and initial conditions from both versions of CCSM4 show smaller biases versus evaluation data sets than does CCSM4 over western North America. WRF simulations also improve spatial details of precipitation over much of North America. However, driving the WRF with the bias‐corrected CCSM4 does not always reduce the bias. WRF‐projected changes in precipitation include decreasing intensity over the southwestern United States, increasing intensity over the eastern United Sates and most of Canada, and an increase in the number of days with heavy precipitation over much of North America. Projected precipitation changes are more evident in the late 21st century than the mid 21st century, and they are more evident under RCP 8.5 than under RCP 4.5 in the late 21st century. Uncertainties in the projected changes in precipitation due to different warming scenarios are non‐negligible. Differences in summer precipitation changes between WRF and CCSM4 are significant over most of the United States.

Climate change assessment for a small island: a Tahiti downscaling experiment

This study addresses the projected 21st century changes in austral summer precipitation and future precipitation anomalies related to El Nino Southern Oscillation (ENSO) for a South Pacific island: Tahiti, French Polynesia. An approach involving 2 successive downscaling steps is proposed here as a first attempt to simulate precipitation over a small orographic island. First, the 50 km mesh global atmospheric model ARPEGE is forced by bias-corrected sea surface temperatures (SSTs) from a CMIP5 scenario. This model drives the limited area model ALADIN. The final 12 km mesh regional simulation coarsely captures the island of Tahiti. Historical and scenario runs (RCP4.5 an d RCP8.5) are therefore available at the island scale. Linking station data and historical model outputs using quantile-quantile plots allows a correction of the biases of the regional simulation and an assessment of precipitation changes over the 21st century. For both scenarios, mean austral summer precipitation tend to increase over the century on the south-east side of Tahiti, following the present El Nino-like precipitation pattern. This trend could be a local manifestation of the large-scale drift of the tropical Pacific Ocean towards an El Nino-like spatial structure. This drift is indeed verified in the SST fields. Then, superimposed upon this slowly evolving mean state, future El Nino events would cause positive precipitation anomalies, whereas future La Nina events would cause negative precipitation anomalies. However, in the last period of RCP8.5, future El Nino events do not seem to affect precipitation anymore, suggesting a damping of the warm events, probably due to a warmer mean state.

Changes of Early Summer Precipitation in the Korean Peninsula and Nearby Regions Based on RCP Simulations

Abstract In this study, the projected regional precipitation changes over northeast Asia (NEA) during early summer [May–July (MJJ)] for the late twenty-first century (2071–2100) were investigated using a high-resolution regional climate model (WRF3.4) based on the representative concentration pathways (RCPs) induced by the global circulation model (HadGEM2-AO). The increased horizontal resolution of the regional model with a 12.5-km horizontal resolution enabled it to reproduce the terrain-following features reasonably well compared to low-resolution reanalysis and HadGEM2-AO model data. The results of a regionally downscaled historical (1981–2010) experiment (D_Historical) demonstrated the model’s ability to capture the spatial and temporal variations of rainband migrating meridionally during MJJ over NEA. According to the regional model projection, intensive precipitation will increase and the rainband will affect the Korean Peninsula approximately 10 days earlier than in the D_Historical cases in both RCP4.5 and RCP8.5 (2071–2100). The precipitation will also increase in most of the domain, particularly in the southern Korean Peninsula and Kyushu, Japan. These increases in precipitation are attributed to increases in the northward moist transport coming from the lower latitudes and moist static instability in the lower atmosphere. According to this study, the convective precipitation contributes mainly to the increase in total precipitation. On the other hand, the large-scale nonconvective precipitation related to the stationary front will not change significantly but even tends to decrease approximately from the middle of July. The extreme precipitation intensity is also projected to increase by at least 22% (38%) in RCP4.5 (RCP8.5).

Astronomical and glacial forcing of East Asian summer monsoon variability

The dynamics of glacial–interglacial monsoon variability can be attributed to orbitally induced changes in summer insolation and internal boundary conditions. However, the relative impacts of astronomical and internal factors on East Asian summer monsoon variability remain controversial. Here we combine proxy data and model results to evaluate the response of East Asian summer monsoon change to these forcings. δ13C of loess carbonate, a sensitive summer monsoon proxy from the western Chinese Loess Plateau, demonstrates coexistence of distinct 100-, 41- and 23-ka periods, in contrast to precession-dominated speleothem δ18O records in South China. Model results indicate that insolation, ice and CO2 have distinct impacts on summer precipitation changes in East Asia, whereas their relative impacts are spatially different, with a relatively stronger insolation effect in south China and a more dominant ice/CO2 influence in north China. Combined proxy data and model results indicate that East Asian summer monsoon variability was induced by integrated effects of summer insolation and changing boundary conditions (e.g., ice sheets and CO2 concentration). Our proxy-model comparison further suggests that gradual weakening of the summer monsoon related to slowly decreasing summer insolation at astronomical timescales will be likely overwhelmed by the projected ongoing anthropogenic CO2 emissions.

Recent changes in summer precipitation in Northeast China and the background circulation

ABSTRACTThis study documents recent changes in the characteristics of summer (July–August–September) precipitation in Northeast China (NEC). A significant shift to less precipitation occurred in 1999–2012 as compared with that in 1984–1998. The reduced precipitation in the later period is closely associated with the large‐scale anomalous high pressure over East Asia and anomalous descending motion over NEC. Furthermore, the significant reductions in the total cloud cover and moisture content also contribute to the reduced precipitation over NEC. To investigate the possible mechanism for the decadal shift of summer precipitation, a northeast Asian summer monsoon (NEASM) index is defined to describe the monsoon circulation over NEC. The results indicate that the NEASM has weakened since 1999 and is concurrent with the shift of the Pacific Decadal Oscillation (PDO) to the negative phase. Warming sea surface temperature (SST) in the North Pacific can zonally reduce the land‐sea thermal contrast and lead to a weak NEASM. Further investigation indicates that the negative phase of the PDO has significant impacts on the atmospheric circulation associated with the NEASM. Additionally, changes in synchronous Arctic sea ice cover (SIC) also likely induce an anomalous sinking movement and weaken water vapour transport; thus, the summer precipitation over NEC decreases.

Changes in East Asian summer monsoon precipitation during the Holocene deduced from a freshwater flux reconstruction of the Changjiang (Yangtze River) based on the oxygen isotope mass balance in the northern East China Sea

Abstract. The δ18O of seawater (δ18Ow), an indirect indicator of sea surface salinity (SSS), in the northern East China Sea (ECS) is reconstructed for the Holocene using paired analyses of Mg / Ca ratio and δ18O of planktic foraminiferal tests. According to modern observation, interannual variations in SSS during summer in the northern ECS are mainly controlled by the Changjiang (Yangtze River) discharge, which reflects summer rainfall in its drainage basin. Thus, changes in the summer SSS in the northern ECS are interpreted as reflecting variations in the East Asian summer monsoon (EASM) precipitation in the Changjiang Basin. This interpretation is confirmed by a strong relationship between the SSS in the northern ECS and the Changjiang discharge during the wet season (May–October) based on instrumental salinity records from 1951 to 2000. However, it is difficult to estimate absolute salinity values in the past with high accuracy, because the past salinity–δ18Ow regression slope, end member salinity, and δ18Ow values are not well understood. Here, we conduct δ18Ow mass-balance calculation to estimate the freshwater contribution to the surface water of the northern ECS during the last 7 kyr by assuming a simple mixing between two end members – the seawater and the Changjiang freshwater. The result indicates that there has been no gradual decreasing secular trend in the Changjiang freshwater flux from the middle Holocene to the present day, suggesting that summer insolation in the Northern Hemisphere does not regulate the EASM precipitation in the Changjiang Basin. Instead, internal feedback appears to have been more important during the Holocene. The absence of a decreasing trend in regional summer precipitation over the Changjiang Basin since the middle Holocene is contradictory to Chinese speleothems' δ18O records, suggesting that it is not possible to explain orbital changes in Chinese speleothems' δ18O during the Holocene by changes in summer precipitation, but that such changes are related to other factors such as changes in the moisture source.

Projected change in East Asian summer monsoon by dynamic downscaling: Moisture budget analysis

The summer monsoon considerably affects water resource and natural hazards including flood and drought in East Asia, one of the world’s most densely populated area. In this study, we investigate future changes in summer precipitation over East Asia induced by global warming through dynamical downscaling with the Weather Research and Forecast model. We have selected a global model from the Coupled Model Intercomparison Project Phase 5 based on an objective evaluation for East Asian summer monsoon and applied its climate change under Representative Concentration Pathway 4.5 scenario to a pseudo global warming method. Unlike the previous studies that focused on a qualitative description of projected precipitation changes over East Asia, this study tried to identify the physical causes of the precipitation changes by analyzing a local moisture budget. Projected changes in precipitation over the eastern foothills area of Tibetan Plateau including Sichuan Basin and Yangtze River displayed a contrasting pattern: a decrease in its northern area and an increase in its southern area. A local moisture budget analysis indicated the precipitation increase over the southern area can be mainly attributed to an increase in horizontal wind convergence and surface evaporation. On the other hand, the precipitation decrease over the northern area can be largely explained by horizontal advection of dry air from the northern continent and by divergent wind flow. Regional changes in future precipitation in East Asia are likely to be attributed to different mechanisms which can be better resolved by regional dynamical downscaling.

Influence of Pacific-Indian Ocean SSTA on Interannual Variation of Summer Precipitation in Shaanxi

Based on the Shaanxi summer precipitation data from 1961 to 2008,NOAA monthly sea surface temperature( SST),NCEP / NCAR monthly global reanalysis data,the relationship between early to the same period in different seasons of the Pacific,Indian Ocean and Shaanxi summer precipitation was analyzed using regression method,SVD method and the cross wavelet analysis method in order to provide clues and foundation for Shaanxi climate prediction. The results showthat: The correlation between Shaanxi summer precipitation with central eastern equatorial Pacific and the western Indian Ocean SST in early autumn and winter is positive,and with North Pacific SST is negative. The distribution of SST correlation coefficient is El Nino SST distribution. To the summer over the same year,the significant positive correlation zone move westward to the eastern Indian Ocean and the eastern coastal of China. The significant regions of influence of Pacific-Indian Ocean SSTA on Shaanxi summer precipitation over Preperiod and the same period locate in Guanzhong and the southeast of Shaanxi. The winter Nino3 SST and Shaanxi summer precipitation has the same phase resonance cycle in the 4 ~ 5 years scale and Nino3 SST ahead of the Shaanxi summer precipitation change is about 4 ~ 6 months. The correlations between East Asia,the South China Sea,Southeast Asia summer monsoon index and Shaanxi summer precipitation and Nino3 SST is all negative. When early Nino3 SST is abnormally high,the East Asian summer monsoon weakened,the Western Pacific subtropical high is stronger and more west,it always appears anomalies southwest wind water vapor transport in southern of Shaanxi,and appears anomalies north wind in northern of Shaanxi Province; the confluence of the warm and cold wind flowin Shaanxi cause more summer precipitation in Shaanxi Province,otherwise summer precipitation in Shaanxi less.

Changes of summer precipitation in China: The dominance of frequency and intensity and linkage with changes in moisture and air temperature

AbstractUsing observed precipitation and the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis, the changes in the metrics of the summer precipitation in China, the dominance of frequency and intensity of daily extreme precipitation, and the linkage with changes in moisture and air temperature are explored. Results show that over the recent 50 years, the total summer rainfall increased over the southeast and the west and decreased over the northeast. The changes in the frequency, identified with the 95% threshold and Poisson regression, and rainfall extremes show similar spatial patterns. The relative importance of the changes in frequency and intensity in the variability and changes in extreme precipitation are estimated. It is shown that, while the interannual variability of the rainfall amount is dominated by the frequency change in almost all stations, the long‐term change of rainfall amount can be dominated by both frequency and intensity, depending on the station. The change in the rainfall total is linked to changes in atmospheric moisture and temperature. The results show that the variability and change of the rainfall total can be dominated by changes in both moisture and air temperature, and the relative importance depends on the region.

Assessing the impacts of climate change on river flows in England using the UKCP09 climate change projections

Summary This paper presents an assessment of the effects of climate change on river flow regimes in representative English catchments, using the UKCP09 climate projections. These comprise a set of 10,000 coherent climate scenarios, used here (i) to evaluate the distribution of potential changes in hydrological behaviour and (ii) to construct relationships between indicators of climate change and hydrological change. The study uses six catchments, and focuses on change in average flow, high flow (Q5) and low flow (Q95). There is a large range in hydrological change in each catchment between the plausible UKCP09 climate projections, with differences between catchments largely due to differences in catchment geology and baseline water balance. The range in change between the UKCP09 projections is in most catchments smaller than the range between changes with scenarios based on the CMIP3 ensemble of climate models (although the shape of the distribution of changes is different), and earlier UK scenarios produce changes that tend towards the lower (drier) end of the UKCP09 range. The difference between emissions scenarios is small compared to the range across the 10,000 scenarios. Changes in high flows are largely driven by changes in winter precipitation, whilst changes in low flows are determined by changes in summer precipitation and temperature.

Analysis of future precipitation in the Koshi river basin, Nepal

We analyzed precipitation projections for the Koshi river basin in Nepal using outputs from 10 General Circulation Models (GCMs) under three emission scenarios (B1, A1B and A2). The low resolution future precipitation data obtained from the GCMs was downscaled using the statistical downscaling model LARS-WG. The data was downscaled for 48 stations located in the six physiographic regions in the Koshi basin. The precipitation projections for three future periods, i.e. 2020s, 2055s and 2090s, are presented using empirical Probability Density Functions (PDFs) for each physiographic region. The differences between the mean values of individual GCM projections and the mean value of the multi-model for the three scenarios allow for the estimation of uncertainty in the projections. We also analyzed the precipitation of the baseline and future periods using six indices that are recommended by the Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI). Results indicate that not all GCMs agree on weather changes in precipitation will be positive or negative. A majority of the GCMs and the average values of all the GCMs for each scenario, indicate a positive change in summer, autumn and annual precipitation but a negative change in spring precipitation. Differences in the GCM projections exist for all the three future periods and the differences increase with time. The estimated uncertainty is higher for scenario A1B compared to B1 and A2. Differences among scenarios are small during the 2020s, which become significant during the 2055s and 2090s. The length of the wet spell is expected to increase, whereas the length of the dry spell is expected to decrease in all three future periods. There is a large scatter in the values of the indices: number of days with precipitation above 20 mm, 1-day maximum precipitation, 5-day maximum precipitation, and amount of precipitation on the days with precipitation above 95th percentile, both in direction and magnitude of the change.

Effect of Climate Change on the Hydrological Character of River Maros, Hungary-Romania

Abstract It is highly probable that the precipitation and temperature changes induced by global warming projected for the 21st century will affect the regime of Carpathian Basin rivers, e.g. that of River Maros. As the river is an exceptionally important natural resource both in Hungary and Romania it is necessary to outline future processes and tendencies concerning its high and low water hydrology in order to carry out sustainable cross-border river management. The analyses were based on regional climate models (ALADIN and REMO) using the SRES A1B scenario. The modelled data had a daily temporal resolution and a 25 km spatial resolution, therefore beside catchment scale annual changes it was also possible to assess seasonal and spatial patterns for the modelled intervals (2021- 2050 and 2071-2010). Those periods of the year are studied in more detail which have a significant role in the regime of the river. The study emphasizes a decrease in winter snow reserves and an earlier start of the melting period, which suggest decreasing spring flood levels, but also a temporally more extensive flood season. Changes in early summer precipitation are ambiguous, and therefore no or only slight changes in runoff can be expected for this period. Nevertheless, it seems highly probable that during the summer and especially the early autumn period a steadily intensifying water shortage can be expected. The regime of the river is also greatly affected by human structures (dams and reservoirs) which make future, more detailed modelling a challenge.

Summer precipitation changes over the Yangtze River Valley and North China: Simulations from CMIP3 models

We present a study of summer precipitation changes over the Yangtze River Valley (YRV) and North China (NC) simulated from 20 models of the CMIP3 (phase 3 of the Coupled Model Intercomparison Project). It is found that the LASG-FGOALS-g1.0 (fgoals) model has the highest ability in simulating both the interannual variability of individual regions and the seesaw pattern of the two regions observed during the past few decades. Analyses of atmospheric circulations indicate that the variability in precipitation is closely associated with the 850 hPa meridional winds over the two regions. Wetness in the YRV and dryness in NC are corresponding to strong meridional wind gradient and weak meridional wind over these two regions, respectively. The ability of a coupled general circulation model (CGCM) to simulate precipitation changes in the YRV and NC depends on how well the model reproduces both observed associations of precipitation with overlying meridional winds and observed meridional wind features in summer. Analysis of future precipitation changes over the two regions projected by the fgoals model under the IPCC scenarios B1 and A1B suggests a significant increase of 7-15% for NC after 2040s due to the strengthened meridional winds, and a slight increase over the YRV due to less significant intensification of the Mei-yu front.

A Framework for Evaluating Model Credibility for Warm-Season Precipitation in Northeastern North America: A Case Study of CMIP5 Simulations and Projections

AbstractFuture projections of northeastern North American warm-season precipitation [June–August (JJA)] indicate substantial uncertainty. Atmospheric processes important to the northeast-region JJA precipitation are identified and a first evaluation of the ability of five phase 5 of the Coupled Model Intercomparison Project (CMIP5) models to simulate these processes is performed. In this case study, the authors develop a set of process-based analyses forming a framework for evaluating model credibility in the northeast region. This framework includes evaluation of models’ ability to simulate observed spatial patterns and amounts of mean precipitation; dynamical atmospheric circulation features, moisture transport, and moisture divergence important to interannual precipitation variability; long-term trends; and SST patterns important to northeast-region summer precipitation.Wet summers in the northeast region are associated with 1) negative 500-hPa geopotential height anomalies centered near the Great Lakes; 2) positive 500-hPa geopotential height anomalies over the western Atlantic east of the Mid-Atlantic states; 3) northeastward moisture flow and increased moisture convergence along the Eastern Seaboard; 4) increased moisture divergence off the U.S. Southeast coast; and 5) positive sea level pressure (SLP) anomalies in the western Atlantic, possibly related to cold tropical Atlantic SSTs and southwest ridging of the North Atlantic anticyclone. Models are generally able to simulate these features but vary compared to observations. Models capture regional moisture transport and convergence anomalies associated with wet summers reasonably well, despite errors in simulating the climatology. Identifying sources of intermodel differences in future projections is important, determining processes relevant for model credibility. In particular, changes in moisture divergence control the sign of northeast-region summer precipitation changes, making it a critical component of process-level analyses for the region.

Greenhouse Gas–Induced Changes in Summer Precipitation over Colorado in NARCCAP Regional Climate Models*

Abstract Precipitation changes between 32-yr periods in the late twentieth and mid-twenty-first centuries are investigated using regional climate model simulations provided by the North American Regional Climate Change Assessment Program (NARCCAP). The simulations generally indicate drier summers in the future over most of Colorado and the border regions of the adjoining states. The decrease in precipitation occurs despite an increase in the surface specific humidity. The domain-averaged decrease in daily summer precipitation occurs in all of the models from the 50th through the 95th percentile, but without a clear agreement on the sign of change for the most extreme (top 1% of) events.

Near future (2016-40) summer precipitation changes over China as projected by a regional climate model (RCM) under the RCP8.5 emissions scenario: Comparison between RCM downscaling and the driving GCM

Multi-decadal high resolution simulations over the CORDEX East Asia domain were performed with the regional climate model RegCM3 nested within the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2). Two sets of simulations were conducted at the resolution of 50 km, one for present day (1980–2005) and another for near-future climate (2015–40) under the Representative Concentration Pathways 8.5 (RCP8.5) scenario. Results show that RegCM3 adds value with respect to FGOALS-g2 in simulating the spatial patterns of summer total and extreme precipitation over China for present day climate. The major deficiency is that RegCM3 underestimates both total and extreme precipitation over the Yangtze River valley. The potential changes in total and extreme precipitation over China in summer under the RCP8.5 scenario were analyzed. Both RegCM3 and FGOALS-g2 results show that total and extreme precipitation tend to increase over northeastern China and the Tibetan Plateau, but tend to decrease over southeastern China. In both RegCM3 and FGOALS-g2, the change in extreme precipitation is weaker than that for total precipitation. RegCM3 projects much stronger amplitude of total and extreme precipitation changes and provides more regional-scale features than FGOALS-g2. A large uncertainty is found over the Yangtze River valley, where RegCM3 and FGOALS-g2 project opposite signs in terms of precipitation changes. The projected change of vertically integrated water vapor flux convergence generally follows the changes in total and extreme precipitation in both RegCM3 and FGOALS-g2, while the amplitude of change is stronger in RegCM3. Results suggest that the spatial pattern of projected precipitation changes may be more affected by the changes in water vapor flux convergence, rather than moisture content itself.

Spring and summer precipitation changes from 1880 to 2011 and the future projections from CMIP5 models in the Yangtze River Basin, China

Precipitation changes in spring (MAM) and summer (JJA) over the Yangtze River Basin during 1880–2011 were analyzed based on observation datasets from 21 gauge stations. The projected changes in precipitation were evaluated using nine Coupled Model Intercomparison Project Phase 5 (CMIP5) datasets. The results suggest that interannual and interdecadal changes in spring and summer precipitation occurred during 1880–2011. The Dry–Dry events of seasonal evolution generally occurred over the past 132 years. Empirical mode decomposition (EMD) was applied to detect the oscillation periods, in which quasi – 3a, 5a, 15a, and 40a periods of spring and quasi – 3a, 5a, 11a, 22a, and 40a periods of summer were identified. S-EOF analysis was employed to identify the major modes of seasonal precipitation evolution from spring to summer. The abnormal location of the western Pacific subtropical high (WPSH) and insufficient water vapor was found to be associated with the 2011 spring drought, and their sudden change is also responsible for the flood in June. A Taylor diagram showed an improved capability to simulate monthly precipitation using the nine CMIP5 datasets. The projected precipitation changes show that the significant positive linear trends of spring precipitation will occur at representative concentration pathways (RCP)2.6 and RCP8.5, whereas summer precipitation will mainly undergo interannual change. For the projected spatial pattern of precipitation anomaly, spring precipitation will increase in the northern basin but decrease in the south under RCP2.6 and RCP8.5 in the 2020s and 2040s. Under RCP4.5, positive anomalies can be found in the middle and lower basins. In contrast to those in the spring pattern, the negative anomalies of summer precipitation are concentrated in the middle and lower basins under each RCP.

“North drying and south wetting” summer precipitation trend over China and its potential linkage with aerosol loading

Changes in summer precipitation over China and their linkage to aerosol loading during 1957–2008 were analyzed. Increased (decreased) summer precipitation has been observed over the Southern (Northern) China, presenting a “north drying and south wetting” pattern. Such a change in precipitation pattern is related to the decreased summertime temperature over South-central China (cool zone). The cool zone, in turn, is likely caused by the increased aerosol loading, as manifested by the increased Aerosol optical depth (AOD) over this region. The cooling effect in the cool zone together with steady warming over adjacent oceans (the South China Sea and the Western North Pacific) weaken land–sea temperature contrast, and thus the East Asia summer monsoon (EASM) circulation. The weakened EASM might restrain the rainbelt in southern China longer with less moisture penetrating further north in summer season. Our analysis suggests that the aerosol loading induced “cool zone” could contribute to the “north drying with south wetting” pattern over Eastern China by altering the intensity of EASM. Furthermore, this change in precipitation pattern is also reflected in the trend of Palmer Drought Severity Index in Eastern China, which indicates a more extensive tendency of dryness in Eastern China by considering both precipitation and temperature.

Effects of Manipulated Precipitation and Shading on Cassiope tetragona Growth and Carbon Isotope Discrimination: A High Arctic Field Study

The reliability of Cassiope tetragona as temperature proxy might be restricted by influence on growth of precipitation and amount of Photosynthetically Active Radiation (PAR). Carbon-13 discrimination (Δ) in C3-plants is generally influenced by temperature and precipitation and can therefore potentially record important additional climatic information.We doubled precipitation and reduced PAR ( -43%), during four and two growing seasons, respectively, at a high arctic site in Svalbard. Differences in discrimination in leaves from separate light, and thus temperature, regimes (sun-facing and soil-facing leaves) were also assessed. A Δ-chronology (1975–2008) in annual shoot length increments was developed. C. tetragona growth did not respond to enhanced precipitation and only slightly to PAR-reduction. Discrimination against carbon-13 was stronger in leaves and shoots receiving extra precipitation and weaker in sun-exposed leaves compared to soil-facing leaves. The annual climate signal in the Δ-chronology was strongly smoothed by secondary radial growth.Our results show that the temperature signal in C. tetragona is hardly disturbed by changes in summer precipitation or PAR, which confirms its suitability as temperature proxy. The experimental evidence for the sensitivity of carbon-13 discrimination in C. tetragona to precipitation and temperature changes shows its potential as proxy for hydrological changes in the polar semi-desert.

Drought and spring cooling induced recent decrease in vegetation growth in Inner Asia

The response of vegetation growth to current climate change in Inner Asia (35–55°N, 45–120°E) was investigated by analyzing time series of the Normalized Difference Vegetation Index (NDVI) data from the Advanced Very High Resolution Radiometer (AVHRR) from 1982 to 2009. We found that at the regional scale, the greening trend observed during the 1980s was stalled in the 1990s. Different seasons, however, show different changes and mechanisms. Among the three seasons (spring, summer and autumn), summer has the earliest turning point (from greening to non-greening) in the early 1990s, as a result of summertime droughts, as indicated by Palmer Drought Severity Index (PDSI). Consistent with the change in summer NDVI, summer PDSI and precipitation significantly increased in the 1980s, but strongly decreased since the early 1990s at the regional scale. The negative effect of summer drought is particularly significant over dry regions such as eastern Kazakhstan, Mongolia and Inner Mongolia. However, in high altitude or high latitude regions (>50°N), summer vegetation growth is more strongly correlated with summer temperature rather than with summer PDSI. In spring, changes in vegetation growth are closely linked with temperature changes rather than droughts. Both spring temperature and spring NDVI, for instance, increased until the late 1990s and then decreased. Statistical analyses also show that spring NDVI is significantly correlated with spring temperature at the regional scale (P<0.05), implying that temperature is the dominant limiting factor for spring vegetation growth in most regions of Inner Asia except Turkmenistan and Uzbekistan, where spring PDSI shows significant positive correlation with spring NDVI. Further analyses of the response of vegetation to extreme high spring temperature in 1997 and extreme summer drought in 2001 exhibit a highly heterogeneous pattern.