Hai He

Spatio-temporal analysis of drought in a typical plain region based on the soil moisture anomaly percentage index

Drought strongly affects the agricultural economy, most severely in plain regions, with prosperous agricultural development, which suffer huge economic losses. An effective index is required to describe the process of drought initiation, development, and alleviation, and soil moisture is a vital variable with respect to agricultural drought as a comprehensive variable. In this study, Jiangsu province was selected as a typical plain region, the VIC (Variable Infiltration Capacity) model was used to simulate soil moisture at a resolution of 0.125°×0.125°, and the soil moisture anomaly percentage index (SMAPI) was established for drought identification and investigation of drought spatio-temporal characteristics between 1956 and 2011. The results show that the VIC model built in our study is feasible, and the simulated 3-layer daily soil moisture database can be used in drought studies as an alternative to measured soil moisture. The droughts in the northern part of the province are more severe than those in the southern part, and Xuzhou is the most frequently affected city. There are no strong trends of drought duration in 13 cities of Jiangsu province. Among the 13 cities, drought intensity decreases as drought duration increases for the same drought area, and drought intensity decreases with drought area for the same drought duration. The methods used here in our study to build the VIC model for plain regions that lack closed basin hydrologic data may be helpful for further studies of VIC, and the regional analysis of drought can provide a powerful reference for regional drought prevention and resistance in Jiangsu province.

Understanding Atmospheric Anomalies Associated With Seasonal Pluvial‐Drought Processes Using Southwest China as an Example

Seasonal pluvial-drought transition processes are unique natural phenomena. To explore possible mechanisms, we considered Southwest China (SWC) as the study region and comprehensively investigated the temporal evolution or spatial patterns of large-scale and regional atmospheric variables with the simple method of Standardized Anomalies (SA). Some key procedures and results include: (1) Because regional atmospheric variables are more directly responsible for the transition processes, we investigate it in detail. The temporal evolution of net vertical integral water vapor flux (net VIWVF) across SWC, together with vertical SA-based patterns of regional horizontal divergence (D) and vertical motion (ω), coincide well with pluvial-drought transition processes. (2) With respect to large-scale circulation patterns, a well-organized Eurasian (EU) Pattern is one important feature during the pluvial-drought transitions over SWC. (3) Based on these large-scale and regional atmospheric anomalous features, relevant SA-based indices were built, to explore the possibility of simulating drought development using previous pluvial anomalies. As a whole, simulated drought development only with SA-indices of large-scale circulation patterns does not perform well. Further, it can be improved a lot when SA-based indices of regional D and net VIWVF are introduced. (4) In addition, the potential drought prediction using pluvial anomalies, together with the deep understanding of physical mechanisms responsible for pluvial-drought transitions, need to be further explored.

Improvement of a combination of TMPA (or IMERG) and ground-based precipitation and application to a typical region of the East China Plain

Hydrological model and water resource assessment performance are highly dependent on the quality of the precipitation input, which can be improved by means of the optimal interpolation method for the merged precipitation. However, the traditional first-guess field of satellite precipitation often increases the merging error on account of its inherent bias. Some authors have suggested the need of generating a more accurate first-guess field for the merged precipitation, but the research in this improvement is rarely reported. Therefore, an improved merging method is proposed in this paper in which the precipitation from rain gauges is added to the first-guess field when combining the precipitation estimates of Tropical Rainfall Measuring Mission (TRMM) Multi-Satellite Precipitation Analysis (TMPA) 3B42 with rain gauges in a typical region of the East China Plain, China. Furthermore, the influence of the gauge station densities on the merged accuracy of the precipitation is investigated based on the traditional and improved methods. The results show that the improved merging method has effectively reduced the influence of the uncertainty caused by the error of the first-guess field owing to the consideration of the spatial distribution of TMPA precipitation and the precision of the gauge precipitation. Compared with results of traditional interpolation methods using only gauge data, the precipitation-merging method in this study can obtain better performance results only when the observation density is lower than 6.0 × 103 km2 per gauge under average conditions of many years. The higher the observation density, the more notably the accuracy increases. In addition, the greater the precipitation, the more homogeneous the spatial and temporal distribution of the precipitation and the better the improved effect of the merging method. The Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement (GPM) mission (IMERG) data is also used to validate the conclusions here.

Hydrologic Evaluation of Multi-Source Satellite Precipitation Products for the Upper Huaihe River Basin, China

To evaluate the performance and hydrological utility of merged precipitation products at the current technical level of integration, a newly developed merged precipitation product, Multi-Source Weighted-Ensemble Precipitation (MSWEP) Version 2.1 was evaluated in this study based on rain gauge observations and the Variable Infiltration Capacity (VIC) model for the upper Huaihe River Basin, China. For comparison, three satellite-based precipitation products (SPPs), including Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) Version 2.0, Climate Prediction Center MORPHing technique (CMORPH) bias-corrected product Version 1.0, and Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) 3B42 Version 7, were evaluated. The error analysis against rain gauge observations reveals that the merged precipitation MSWEP performs best, followed by TMPA and CMORPH, which in turn outperform CHIRPS. Generally, the contribution of the random error in all four quantitative precipitation estimates (QPEs) is larger than the systematic error. Additionally, QPEs show large uncertainty in the mountainous regions, with larger systematic errors, and tend to underestimate the precipitation. Under two parameterization scenarios, the MSWEP provides the best streamflow simulation results and TMPA forced simulation ranks second. Unfortunately, the CHIRPS and CMORPH forced simulations produce unsatisfactory results. The relative error (RE) of QPEs is the main factor affecting the RE of simulated streamflow, especially for the results of Scenario I (model parameters calibrated by rain gauge observations). However, its influence on the simulated streamflow can be greatly reduced by recalibration of the parameters using the corresponding QPEs (Scenario II). All QPEs forced simulations underestimate the streamflow with exceedance probabilities below 5.0%, while they overestimate the streamflow with exceedance probabilities above 30.0%. The results of the soil moisture simulation indicate that the influence of the precipitation input on the RE of the simulated soil moisture is insignificant. However, the dynamic variation of soil moisture, simulated by precipitation with higher precision, is more consistent with the measured results. The simulation results at a depth of 0–10 cm are more sensitive to the accuracy of precipitation estimates than that for depths of 0–40 cm. In summary, there are notable advantages of MSWEP and TMPA with respect to hydrological applicability compared with CHIRPS and CMORPH. The MSWEP has a greater potential for basin–scale hydrological modeling than TMPA.

High-Resolution Dynamical Downscaling of Seasonal Precipitation Forecasts for the Hanjiang Basin in China Using the Weather Research and Forecasting Model

AbstractManagement of water resources may benefit from seasonal precipitation forecasts, but for obtaining high enough resolution, dynamical downscaling is necessary. This study investigated the downscaling capability of the Weather Research and Forecasting (WRF) Model ARW, version 3.5, on seasonal precipitation forecasts for the Hanjiang basin in China during 2001–09, which was the water source of the middle route of the South-to-North Water Diversion Project (SNWDP). The WRF Model is forced by the National Centers for Environmental Prediction Operational Climate Forecast System, version 2 (CFSv2), and it performs at a high horizontal resolution of 10 km with four selected convection schemes. The National Oceanic and Atmospheric Administration’s Climate Prediction Center global daily precipitation data were employed to evaluate the WRF Model on multiple scales. On average, when large biases were removed, the WRF Model slightly outperformed the CFSv2 in all seasons, especially summer. In particular, the K...