Long-term trend analysis on total and extreme precipitation over Shasta Dam watershed

ABSTRACTThe regional features of long‐term changes in total and extreme precipitations over eight China domains and their seasonality and relationships with large‐scale and local atmospheric and oceanic factors are investigated. A newly compiled data set of 917 China stations from the China National Meteorological Information Center with strict quality control is analysed. Wintertime extreme precipitation has increased persistently in all China domains, together with an obvious wetting tendency except in North China. In spring, an increase in extreme precipitation is also seen except in South China, but total precipitation increases only in half of China. A ‘northern drying and southern wetting’ (NDSW) pattern is found over eastern China for both extreme and total precipitations in summer when precipitation increases significantly in Northwest China (NWCH). Different features are found in autumn when negative trends are found in most of the China domains for total precipitation (except in NWCH and the Tibetan Plateau) and half of the domains for extreme precipitation. Overall, the frequency of extreme precipitation plays a dominant role in determining the extreme precipitation trend compared to the intensity of precipitation. The long‐term changes in total precipitation and extreme ratio (extreme precipitation to total precipitation) are both strongly linked to the sea surface temperatures (SSTs) from the Indian Ocean to the Maritime Continent, the Kuroshio, the central‐eastern Pacific, and part of the Atlantic Ocean. In summer, the NDSW pattern is closely associated with the weakening of East Asian monsoon circulation and the increase in land surface temperature of 40°–60°N. Local warming trends also contribute to the trends of extreme ratio in several domains in particular seasons.

Few states depend more on climatic stability than California. While the California water system is designed fairly well to accommodate repeats of historical droughts in the near future, there is concern that California might not be able to easily accommodate major droughts in the more distant future, especially with the hydrologic consequences of significant climate warming. This study developed comprehensive surface and ground water hydrologies for 12 climate warming scenarios for California's inter-tied water system, as well as economic water demand estimates for urban and agricultural uses for estimates 2100 population levels. The most severe of these 12 climatic warming hydrologies was then employed with these 2100 economic water demands as inputs into an integrated economic-engineering optimization model of California's inter-tied water system (CALVIN). The results indicate the effects of population growth and climatic change on the performance of California's water system, as well as promising water management strategies to respond to these changes in supply and demand conditions over the coming century.

The assessment of hydrometeorological variables using climate scenario data derived from global climate models (GCMs) is essential for adapting and mitigating climate‐induced changes. However, GCM outputs are too coarse to apply at the basin scale. Therefore, spatial downscaling of GCM outputs has been widely used to assess hydrological changes on the basin scale. Temporal downscaling is also required to obtain hourly precipitation data for small or medium basin analysis because only several hours of data are required to determine peak flows after rainfall. This study presents the spatiotemporal distribution of downscaled hourly precipitation over South Korea for two representative concentration pathway scenarios (RCP4.5 and RCP8.5), as well as its implications over hydrological responses. Under the RCP8.5 scenario, the mean hourly precipitation significantly increases over the southern part of South Korea, especially during the morning, with a smaller increase at later times of the day. However, this increase is not propagated to the mainland because of mountainous areas in the southern part of the country. Furthermore, the hydrological responses determined by a distributed rainfall‐runoff model reveal a significant increase in the peak flow under the RCP8.5 scenario but a slight decrease under the RCP4.5 scenario. In addition, the observed relation between extreme precipitation and temperature is compared with that under RCP8.5. The results indicate that the downscaled hourly precipitation data adequately reproduce the observed relationship. We conclude that the temporal downscaling method used in this study is suitable for obtaining hourly precipitation data from daily GCM scenarios. In addition, rainfall‐runoff simulations using downscaled hourly precipitation data are useful for investigating hydrological response variability related to future climate scenarios.

Rice yield have been affected by the increased extreme precipitation events in recent decades. Yet, the spatio-temporal patterns of extreme precipitation by rice type and phenology remain elusive. Here, we investigate the characteristics of four extreme precipitation indices across China’s rice paddy and their potential association with crop yields, by using hourly precipitation data from 1,215 stations and rice phenology observations from 45 sub-regions. The data indicate that hourly extreme precipitation have significantly increased in 1961–2012 for single rice and early rice in China but not for late rice. Rice were mainly exposed to extreme precipitation from transplantation to flowering stages. The frequency and proportion of extreme precipitation were significantly increased by 2.0–4.7% and 2.3–2.9% per decade, respectively, mainly in south China and Yangtze River Basin. The precipitation intensity and maximum hourly precipitation were increased by 0.7–1.1% and 0.9–2.8% per decade, respectively, mainly in central China and southeast coastal area. These extreme precipitation indices played a role as important as accumulated precipitation and mean temperature on the interannual variability of rice yields, regardless of rice types. Our results also highlight the urgencies to uncover the underlying mechanisms of extreme precipitation on rice growth, which in turn strengthens the predictability of crop models.

This study is intended to simulate and better understand mean and extreme precipitation over the Loess Plateau (LP) in China using the Weather Research and Forecasting (WRF) model. We performed a long-term (1980–2011) simulation with the WRF model at a 10 km horizontal resolution, forced by the ERA-Interim reanalysis. A series of sensitivity experiments were conducted to investigate the influence of resolution and physical parameterization schemes on the simulation ability of the WRF model over the LP. The region has a dominant semi-arid climate and is adversely affected by extreme precipitation. Results show that the WRF model produced better simulations at a 10 km resolution for the LP with complex terrain than it did at coarser resolutions. WRF simulations for precipitation over the LP were most sensitive to cumulus schemes, moderately sensitive to planetary boundary layer schemes, and less sensitive to microphysics schemes. The WRF model not only adequately captured the spatial distribution of precipitation in the LP but also reproduced its magnitude and variability at different time scales. Moreover, the WRF model captured 73% of the observed extreme precipitation events with an intensity of more than 12 mm day− 1, which cause substantial soil erosion in the LP. Although it was unable to capture 27% of the observed events, the WRF model reasonably reproduced ERA-Interim extreme precipitation and its dynamic processes. These analyses strongly suggest that the biased extreme precipitation generated with the WRF model most likely resulted from inaccurate ERA-Interim forcing data. This study provides a better understanding of extreme precipitation simulations as well as insight into predictions of soil erosion in the LP.

Effect difference of climate change and urbanization on extreme precipitation over the Guangdong-Hong Kong-Macao Greater Bay Area

The extreme daily precipitation in Serbia was examined at 16 stations during the period 1961–2014. Two synoptic situations in May and September of 2014 were analysed, when extreme precipitation was recorded in western and eastern Serbia, respectively. The synoptic situation from 14 to 16 May 2014 remained nearly stationary over the western and central Serbia for the entire period. On 15 May 2014, the daily rainfall broke previous historical records in Belgrade (109.8 mm), Valjevo (108.2 mm) and Loznica (110 mm). Precipitation exceeded 200 mm in 72 h, producing the most catastrophic floods in the recent history of Serbia. In Negotin (eastern Serbia), daily precipitation of 161.3 mm was registered on 16 September 2014, which was the maximum value recorded during the period 1961–2014. The daily maximum in 2014 was registered at 6 out of 16 stations. The total annual precipitation for 2014 was the highest for the period 1961–2014 at almost all stations in Serbia. A non-significant positive trend was found for all precipitation indices: annual daily maximum precipitation, the total precipitation in consecutive 3 and 5 days, the total annual precipitation, and number of days with at least 10 and 20 mm of precipitation. The generalised extreme value distribution was fitted to the annual daily maximum precipitation. The estimated 100-year return levels were 123.4 and 147.4 mm for the annual daily maximum precipitation in Belgrade and Negotin, respectively.

In this study, we conduct a 15‐year long (2008–2022) convection‐permitting simulation over the Tibetan Plateau (TP) using the Weather Research and Forecasting (WRF) model to evaluate its added value compared to ERA5 in characterizing subdaily precipitation and its extremes over the TP. Our findings indicate that the overestimation of precipitation amounts caused by overestimated precipitation frequency in ERA5 is mitigated in WRF mainly through a reduction in light precipitation occurrences. This improvement is likely linked to increased temperatures and decreased relative humidity in the lower troposphere. Moreover, the much earlier precipitation peak in ERA5 is corrected in WRF, a result attributed to differences in related net water vapor transport onto the TP. Additionally, WRF provides a more accurate estimation of the percentage of short‐ and long‐duration precipitation events with only slight underestimations and overestimations, respectively, whereas ERA5 exhibits significantly larger errors. The relatively larger temperature changes in WRF, indicating increased solar heating, are likely responsible for the higher occurrence of short‐duration precipitation events. In contrast, the anticyclonic anomalies and northeastern wind anomalies in WRF reduce the persistence of long‐duration precipitation. Importantly, WRF also produces more realistic timings of precipitation with different durations compared to ERA5. For extreme precipitation, short‐duration extreme events dominate accounting for 50% of extreme precipitation. These events are better reproduced by WRF than by ERA5. Although WRF outperforms ERA5 in estimating the proportion and contribution of extreme events to total precipitation and in capturing their triggering timing, a slight underestimation persists in the simulated proportion and contribution.

Dynamical downscaling is a widely used technique to properly capture regional surface heterogeneities that shape the local hydroclimatology. However, in the context of dynamical downscaling, the impacts on simulation fidelity have not been comprehensively evaluated across many user-specified factors, including the refinements of model horizontal resolution, large-scale forcing datasets, and dynamical cores. Two global-to-regional downscaling methods are used to assess these: specifically, the variable-resolution Community Earth System Model (VR-CESM) and the Weather Research and Forecasting (WRF) Model with horizontal resolutions of 28, 14, and 7 km. The modeling strategies are assessed by comparing the VR-CESM and WRF simulations with consistent physical parameterizations and grid domains. Two groups of WRF Models are driven by either the NCEP reanalysis dataset (WRF_NCEP) or VR-CESM7 results (WRF_VRCESM) to evaluate the effects of large-scale forcing datasets. The simulated hydroclimatologies are compared with reference datasets for key properties including total precipitation, snow cover, snow water equivalent (SWE), and surface temperature. The large-scale forcing datasets are critical to the WRF simulations of total precipitation but not surface temperature, controlled by the wind field and atmospheric moisture transport at the ocean boundary. No significant benefit is found in the regional average simulated hydroclimatology by increasing horizontal resolution refinement from 28 to 7 km, probably due to the systematic biases from the diagnostic treatment of rainfall and snowfall in the microphysics scheme. The choice of dynamical core has little impact on total precipitation but significantly determines simulated surface temperature, which is affected by the snow-albedo feedback in winter and soil moisture estimations in summer.

The daytime and nighttime precipitation proportions of daily total precipitation (especially extreme daily precipitation) are important indicators that help to understand the process of precipitation formation, which in turn helps to evaluate and improve models and reanalysis precipitation data. In this study, we used the Huai River Basin (HRB) as a case to explore the daytime and nighttime precipitation proportions of daily total precipitation based on 135 meteorological stations during 1961–2018. The total, daytime, and nighttime precipitation showed zonal distributions with high and low values in the southern and northern parts of the basin, respectively. The nighttime precipitation was slightly greater than the daytime precipitation. With the increase in precipitation intensity, the seasonal cycles of the total, daytime, and nighttime precipitation were more distinct, and precipitation mainly occurred in summer. The annual range of precipitation differences between daytime and nighttime in wet seasons showed a downward trend in 1961–2003 followed by an upward trend in 2003–2018. This reversal of annual range of precipitation around 2003 may be related to the changes in annual range of convective precipitation differences between daytime and nighttime in wet seasons. The decrease of light precipitation mainly depended on the decrease of nighttime precipitation. The contributions of nighttime precipitation events to torrential precipitation events were greater than those of daytime precipitation. The days of extreme precipitation events accounted for a very low proportion of total precipitation days, but their precipitation amount accounted for relatively high proportions of total precipitation amount. Annual extreme precipitation amount showed a slightly upward trend, which was caused by the increased nighttime precipitation. Under extreme precipitation conditions, large proportions of daytime precipitation were mainly concentrated in the southeastern parts of the HRB, whereas large proportions of nighttime precipitation were mainly concentrated in the northwestern parts of the basin. The concurrent daytime and nighttime precipitation showed slightly increasing trends, especially in the southeastern part of the basin. With the increase in daytime and nighttime precipitation, the risk of concurrent precipitation extremes in the southern part of the basin increased (shorter return period means higher risk).

Impact of different reanalysis data on WRF dynamical downscaling over China

Global warming has profound effects on precipitation patterns, leading to more frequent and extreme precipitation events over the world. These changes pose significant challenges to the sustainable development of socio-economic and ecological environments. This study evaluated the performance of the new generation of the mesoscale Weather Research and Forecasting (WRF) model in simulating long-term extreme precipitation events over the Minjiang River Basin (MRB) of China from 1981 to 2020. We calculated 12 extreme precipitation indices from the WRF simulations and compared them with observations. The spatio-temporal variations of extreme precipitation were further analyzed in terms of intensity, frequency, and duration. The results indicated that the WRF model can appropriately reproduce the spatial distribution of extreme precipitation indices with acceptable biases. The performance is significantly better for intensity and frequency indices compared to duration indices. Except for PRCPTOT and R10mm, WRF accurately captures the interannual variations of extreme precipitation. Meanwhile, the results of the pre-whitening Mann-Kendall (PWMK) test suggested that WRF can identify significant increasing trends in extreme precipitation, particularly for R95p, R99p, and R50mm. This study provides valuable insights for extreme precipitation forecasting and warning in other mountainous regions.

Developing a water-energy-GHG emissions modeling framework: Insights from an application to California's water system

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.

The atmospheric river (AR) is a unique mover of moisture from the low latitudes to mid- and high latitudes and a potential cause for regional flooding. This study explores the ARs’ influence on wintertime precipitation (including extreme precipitation) over the pan-North Pacific during 1996–2018 from the climatological perspective and during the ENSO condition, via distinguishing precipitation and moisture transport between the AR-group and the non-AR-group. Climatologically, the AR-group contributes 30%–45% of total winter precipitation, and up to 70% of total extreme precipitation over the eastern Pacific and along the North American west coast between 25° and 45°N. The above area is the core region of the ARs’ influence on precipitation. The AR-group’s precipitation in the core region is mostly determined by AR-produced in situ moisture convergence, while the non-AR-group’s precipitation is attributed to evaporation from Earth’s surface. The AR frequency is increased (decreased) in the core region during El Niño (La Niña) winters. As a result, the AR-group contributes more than half of the positive (negative) anomalies in total precipitation in the core region, due to AR-related moisture convergence anomalies. Besides, during El Niño winters, the AR-group also contributes almost half of negative anomalies in total precipitation over the middle basin between 40° and 55°N. An anomalous moisture sink (source) always acts to increase (decrease) in situ precipitation for both the AR-group and the non-AR-group. It is also shown that the moisture transport and its divergence anomalies are primarily decided by changes in wind fields and second by moisture. Furthermore, changes in moisture can cause asymmetric features of anomalies in moisture transport and its divergence between El Niño and La Niña but with limited effects.