Statistical Prediction of Wet and Dry Periods in theComahue Region (Argentina)

General features of rainy season with excess or deficits are analyzed using standardized precipitation index (SPI) in Limay and Neuquen River basins. Results indicate that most of dry and wet periods persist less than three months in both basins. Furthermore, an increase of rainfall variability over time is observed in the Limay river basin but it is not detected in the Neuquen river basin. There is a tendency for wet (dry) periods to take place in El Ni?o (La Ni?a) years in both basins. Rainfall in both basins, have an important annual cycle with its maximum in winter. In addition, possible causes of extreme rainy seasons over the Limay River Basin are detailed. The main result is that the behavior of low level precipitation systems displacing over the Pacific Ocean in April influences the general hydric situation during the whole rainy season. In order to establish the existence of previous circulation patterns associated with interannual SPI variability, the composite fields of wet and dry years are compared. The result is that rainfall is related to El Ni?o- Southern Oscillation (ENSO) phenomenon and circulation over the Pacific Ocean. The prediction scheme, using multiple linear regressions, showed that 46% of the SPI variance can be explained by this model. The scheme was validated by using a cross-validation method, and significant correlations are detected between observed and forecast SPI. A polynomial model is used and it little improved the linear one, explaining the 49% of the SPI variance. The analysis shows that circulation indicators are useful to predict winter rainfall behavior.

DRY/WET CLIMATE CHANGE SINCE 960 A.D.IN TAIHU DRAINAGE BASIN OF CHINA

ABSTRACT: The present study reconstructs an annual dry/wet grade series from 960 A. D. to 1992 A. D. in the Tai-hu drainage basin of eastern coast, China by collecting historical climatic records, to examine the climate periodicity and climate jumps. Power Spectrum analysis reveals that the dry/wet climate in the study area was a superposed phenomenon with the major period of quasi-100-year, and several other notable periods. These periods were supposed to be closely linked with the celestial activity. Climate jumps are detected using moving t-test. The two abrupt changes around 1247 - 1263 A. D. and 1618 - 1635 A. D. are proved as regional events. The 14th to 15th century appeared as the wettest period during the last 1000 years in the Taihu drainage basin. These are interpreted as the consequence of east Asia climate change.

Transformation and mechanisms of climate wet/dry change on the northern Tibetan Plateau under global warming:A perspective from paleoclimatology

The northern Tibetan Plateau is a climatically sensitive zone influenced by monsoon and westerly winds.In summer,water vapor transport can reach Qinghai Lake and the eastern section of the Qilian Mountains;in winter,westerly winds mainly control the climate.This article compares the wet/dry changes in the region during the mid-Holocene(MH)warm period,the medieval climate anomaly(MCA),the current warm period(CWP),and the future warm period from the perspective of paleoclimate.We found that the MH warm period was mainly affected by the orbit-controlled East Asian summer monsoon,and the region showed warm and humid climate characteristics.The MCA was mainly controlled by solar radiation,and there was a warm and dry phenomenon.The CWP and the future warm period are mainly controlled by the rise in temperature caused by the increase in greenhouse gases,and the climate is becoming more arid.The wet/dry patterns in the CWP and the future warm period in the next century on the northern Tibetan Plateau are similar to those in the MCA.Continued warming will lead to the expansion of the westerly belt and a gradually humid climate.The future wet/dry changes will be more similar to the MH warm period.

Temporal Dynamics of Standardized Precipitation Evapotranspiration Index and Its Influence to Summer Maize Yield from Kaifeng Region in He’nan Province

Many quantitative studies get more and more attention on drought occurrence and monitoring trends of drought change using different methods;however few studies involve correlation between drought and crop yield especially drought index. This study analyzed the climate change about annual mean SPEI-3, SPEI-6 and SPEI-12, of Kaifeng region in the period of 1961-2013. The SPEI-3 and SPEI-6 seasonal short timescales showed a decreasing tendency, especially rapidly a decline since 2004, and high-frequency alternate dry/wet periods occurred during 1961-2013. However, the annual timescale SPEI-12 showed almost no evidently rise/decline tendency but severity events of dry/wet episode aggravated in terms of duration and magnitude and remarkable low-frequency change. Correlation analysis results between maize yield from Kaifeng region and multi-month scale annual SPEI showed a high negative significant correlation with -0.689 (ρ ρ < 0.001) in June SPEI-3. Further analysis between maize yield and temperature, precipitation and light during June-September found that precipitation in June and August was the main limiting factor to maize yield and their correlation values were well below the correlation of SPEI-3 of June. Finally, the reconstruction equation found that there was a better change consistency between the maize yield reconstruction and actual production but more error in extremely high and low annual yield. This study provides a reliable analysis of climate change to corn yield and basic data support for services of grain production and food security in the future.

基于复合机器学习模型的无线微波降雨反演研究

为实现精细化的无线微波水文气象密集监测,提出基于无线微波链路的降雨增强反演方案。利用极值梯度提升(XGBoost)算法进行干湿判别,并结合支持向量回归机(SVR)和高斯过程回归(GPR)两种机器学习算法,构建XG_SVR与XG_GPR复合反演模型,与传统ITU-R模型反演结果比较分析。实验结果表明,XGBoost算法的干湿判别结果优于滑动标准差法,平均分类准确率为88%,1 h以下高时间分辨率的准确率可达90%以上;两种复合模型整体反演效果良好,XG_SVR与ITU-R模型均适用于高时间分辨率,相关性系数均值皆高于0.80;而XG_GPR模型在反演1 h及以上低时间分辨率降雨时有显著优势,相关性系数为0.95左右,且均方误差远小于其他两种模型。利用复合机器学习模型改进传统无线微波测雨的方案具有可行性及发展潜力。