| The growing observations further confirmed that the global climate change caused byincrease in the concentration of greenhouse gases in the atmosphere has become one of themain problems of the global environment. Global climate change will have a major impact onhydrology and water resources systems, places which as in snowmelt-dominated runoff aremore significantly affected by climate change. Irrigated agriculture is a typical feature of theCalifornia Central Valley region,which is one of the world’s famous and efficient agriculturalproduction areas, irrigation water is heavily dependent on the Sierra Nevada snowmelt, globalwarming and regional climate change will be a significant impact on the area of waterresources systems. The quantitative evaluation of the impact of climate change on hydrologyand water resources systems is the basic work for the sustainable development and utilizationof water resources in the future. It is of great significant to the evolution of specific cognitiveregional hydrological processes, rational development and protection of water resources in theSan Joaquin River Basin, and maintaining the Central Valley of California regionalagricultural sustainable development. In view of this point, we select five sub-basins of SanJoaquin River located in the west side of the Sierra Nevada Mountains of California, on thebasis of building a water cycle model, sensitivity analysis scenarios and GCM downscalingscenarios was build to evaluate hydrological response to the future climate change, In the casestudy, the main findings are as follows:(1) Hydrometeorological factor variation analysis of San Joaquin River watershedupstream region Combined moving-t test, Mann-Kendall, Spearman, Yamamoto test andwavelet transform method to analysis the trend, mutation, and periodical of thehydrometeorological elements in this region. The results show more obvious growth trend ofoverall temperature in the study period, the average annual temperature ramp rate is0.71℃/10a, and showed a significant upward trend in winter temperatures. Significant annual andseasonal changes in precipitation did not occur. While summer runoff reduction or increase inspring runoff, the overall runoff presented in advance during its process. By the statistical analysis, hydrometeorological elements of mutations occurred at around1986in the region,and there are changes in periodical of9-12years and19-22years. Because of North PacificDecadal Oscillation(NPO) climatic characteristics affect the western region of the Americas,atmospheric circulation process is a major factor in affecting California regional climatechange, global atmospheric circulation changes in the process will have a major impact on theregion’s climate.(2) Watershed scale hydrological model construction and its adaptive testing. Based ondepth analysis of the HSPF model structure and its main principles, build ahydro-meteorological and geographical database, utilized man-machine joint parametercalibration method to calibrate the model parameters, and evaluated the sensitivity of themodel parameter. The results show that subsided constant wet bulb temperature, snowmeltcoefficient, daily groundwater recession rate, soil retreat coefficient and saturated hydraulicconductivity were more sensitive parameter, which has a greater impact on watershed runoffprocess. The annual runoff difference during the calibration period varied from9.23%to-18.65%, and varies from9.59to11.69%in the verification period. EC values of the monthlyflow in the calibration and verification period model were0.86and0.97, and the correlationcoefficient were0.906and0.97, respectively. During the calibration and validation period, ECvalues of daily flow were0.771and0.882, corresponding R2value of0.83and0.897,respectively, the statistical test results showed that the daily flow calibration and validationperiod no significant differences. Model better reflects the typical Mediterranean climate andmountain climate characteristics, overall prediction accuracy of the inspection requirements ofthe study area has good adaptability to meet projected needs.(3) The spatial and temporal characteristics of climate change in California and itsdownscaling. the variation of temperature and precipitation trends in the future in the differentregions was analyzed, the results show that the warming trend in the future is more consistent,but no significant changes in trends in precipitation simulation results. California’s coastalmountain will have moderate temperature changes, and more significant change in the SierraNevada, and the Northeast region. Changes in precipitation volatile, sensitive areas are mainlyconcentrated in the northwest coastal areas, the north Sierra Nevada Mountains and along thesouthern coast of California. By downscaling methods based on global climate model (GCM)analysis showed that the headwater area of San Joaquin average daily temperatures measuredvalues and simulation values fitting well, the average daily temperature average coefficient ofthe model simulation period is0.97, but because of factors subject to special areas of theSierra Nevada terrain conditions and weather conditions, the simulation results of theprecipitation statistics weak correlation, the average coefficient is approximately0.76. In the A2scenario, the average temperature change in the next four periods (2030s,2050s,2070s,2090s) are+1.6℃,+2.1℃,+3.7℃and4.2℃; In the B1scenario, the average temperaturechanges are+1.0℃,+1.7℃,+2.3℃and+3.4℃, the average temperature in summer is themost significant changes under the two scenarios, during next four periods, the summeraverage temperature changes were+2.9℃,+3.8℃,+4.7℃and+5.6℃in the A2scenario,and+1.2℃,+1.4℃,+3.6℃. and+4.6℃for B1scenarios respectively, the second forchanges is in winter, spring and fall relatively with small changes.(4) Quantitative analysis of the future impact of climate change on the headwater regionof the San Joaquin River. Using the identified future climate change situation in California,coupled HSPF hydrological model to study the impact of future climate change on watershedrunoff. The incremental scenarios analyzed result showed that annual runoff change intervalsapproximate range from-43.7%to16.8%. If other factors are held constant, risingtemperatures will cause runoff change of-23.7%to-8.3%. In the case of A2, B1, futurechanges in runoff range from-32.3%to19.7%。In A2case, runoff decreases trend is greaterthan B1For month-to-month analysis May to September runoff existence a downward trend,from January to April and November-December month runoff showing an upward trend. Inthe case of seasonal analysis, winter and spring runoff is mainly characterized by anincreasing trend, while the downward trend in summer runoff, with moderate degree ofchange in the fall. In sensitivity analysis cases, under the same circumstances, risingtemperatures caused by runoff (CT value) were moved forward16-45days. Maintain constanttemperatures, precipitation changes lead to changes in CT value is only1-4days. In B1emission scenarios, simulation results show that CT values were13-20days in advance, andin the case A2emission CT values were34-38days in advance, and the rainfall changescaused by changes in CT value is only2-4days, rising temperatures affecting the main factorsof the runoff process. Analysis showed that by contrast, warm and dry climatic characteristicsof the San Joaquin River basin header region in the mid-21st century will be more obvious,which will causing the decreasing trend of annual runoff, the variation of the wet and dryseason is more significant, the seasonal change of runoff enhanced runoff process andsignificant advance in runoff process. |
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