1961-2011年陕西省汛期短时降水变化特征

利用1961-2011年陕西省23个气象站的逐时降水量资料,分析了汛期(5-9月)降水时数、小时雨强、极端强降水时数和极端降水强度的时空变化。结果表明:(1)近51年陕西汛期降水时数的长期变化趋势在空间上不一致,陕北和陕南西部表现为减少趋势,关中大部和陕南东部表现为增多趋势,但降水强度长期变化均呈增强趋势。区域平均降水时数的长期变化趋势不明显,但具有阶段性变化特征,区域平均降水强度在波动中呈增强趋势;(2)陕西极端强降水时数和极端降水强度的长期变化趋势在空间上较为一致,极端强降水时数明显增多,强度明显增强。(3)汛期降水日变化南北不同,陕北午后至傍晚主峰突出,而陕南则早峰明显,关中平原降水日变化相对较小。极端强降水时数和降水量在03:00-10:00(北京时)显著增多,这将增大滑坡、泥石流等灾害的发生风险,尤其是发生在夜间,其危害则更大。

1961—2000年西南地区小时降水变化特征

根据西南地区112个站点1961—2000年逐时降水资料,分析了不同季节降水时数、小时雨强、极端强降水时数和极端强降水强度的变化趋势。从降水时数变化来看,夏季西南大部分地区如四川盆地西部、云南、贵州南部等地总降水时数有减少趋势,四川盆地东部和川西高原总降水时数增加;整个区域平均趋势为-0.9%/10a。相应地,极端强降水时数虽然在盆地西部减少,但在西南大部分地区,特别是四川盆地东部、川西高原、云南大部、贵州增加,区域平均增加趋势为2.0%/10a。秋季西南地区总降水时数整体减少(-3.5%/10a),而极端强降水时数趋势不明显。从雨强变化来看,夏季除盆地西部平均雨强减小外,西南地区大部平均雨强增大,大部分站点极端强降水雨强也增大;秋季平均雨强在云南和贵州大部分地区有增大趋势,而盆地东部和川西高原有减小趋势。

北京地区精细化的降水变化特征

应用2007-2010年北京地区123个数据质量较好的自动气象站逐时降水数据，分析了该地区夏季不同级别降水的空间特征和4～10月降水的时间变化特征。结果表明，北京地区2007-2010年自动站年平均夏季降水量分布与1978-2010年常规站多年平均夏季降水量分布较一致，夏季总降水小时数明显高值中心在北部山区和城区以西山区，小时雨强以东北部、城区为高值中心，自东向西趋势递减，7月城区小时雨强最强。

Changes in Climatic Factors and Extreme Climate Events in Northeast China during 1961-2010

This study focuses on examining the characteristics of climate factors and extreme climate events in Northeast China during 1961- 2010 by using daily data from 104 stations, including surface air temperature, precipitation, wind speed, sunshine duration, and snow depth. Results show that annual mean temperature increased at a significant rate of 0.35℃ per decade, most notably in the Lesser Khingan Mountains and in winter. Annual rainfall had no obvious linear trend, while rainy days had a significant decreasing trend. So, the rain intensity increased. High-temperature days had a weak increasing trend, and low-temperature days and cold wave showed significant decreasing trends with rates of 3.9 d per decade and -0.64 times per decade, respectively. Frequency and spatial scope of low-temperature hazard reduced significantly. Warm days and warm nights significantly increased at 1.0 and 2.4 d per decade, while cold days and cold nights decreased significantly at -1.8 and -4.1 d per decade, respectively. The nighttime warming rate was much higher than that for daytime, indicating that nighttime warming had a greater contribution to the overall warming trend than daytime warming. The annual mean wind speed, gale days, and sunshine duration had significant decreasing trends at rates of-0.21 m s-1 per decade, -4.0 d per decade and -43.3 h per decade, respectively. The snow cover onset dates postponed at a rate of 1.2 d per decade, and the snow cover end date advanced at 1.5 d per decade, which leads to shorter snow cover duration by -2.7 d per decade. Meanwhile, the maximum snow depth decreased at -0.52 cm per decade. In addition, the snow cover duration shows a higher correlation with precipitation than with temperature, which suggests that precipitation plays a more important role in maintaining snow cover duration than temperature.

Characteristics of Drought and Humidification Based on Standardized Precipitation Index in Weifang City during the Past 50 Years

[Objective] This study aimed to analyze the evolution characteristics and occurrence patterns of droughts and floods in Weifang City. [Method] Based on the monthly precipitation data during 1961-2010 obtained from nine meteorological sta- tions of Weifang City, by using standardized precipitation index, monthly SPI index of Weifang City during the past 50 years was calculated to analyze the spatial and temporal distribution characteristics of drought and humidification in Weifang City. [Result] The results showed that the variation of drought and humidification had stage characteristics in Weifang City, which was relatively humid in the 1960s and 1970s and developed from extremely humid in early 1960s to dry in late 1970s, persistent drought was observed throughout the range of Weifang City in the 1980s, and the variation tended to be smooth during the 1990s-2000s. Spatial distribution of drought and humidification in Weifang City showed certain regional characteristics. In the 1960s, the mid-west region of Weifang City was relatively humid, while the southeastern region was relatively dry; in the 1970s, there was little difference among the drought and humidification extent in each region; in the 1980s, each region of Weifang City was generally dry, specifically, drought in the southeastern region was the most severe, while drought in the northern region was the slightest; in the 1990s and 2000s, variation of drought and humidification in each region of Weifang City was basically the same. The uneven spatial and temporal distribution of precipi- tation led to abnormal distribution of drought and humidification in some areas, such as the abnormal phenomenon in 1999; the spatial distribution of drought and humidi- fication duration in each generation had their own characteristics, which brought diffi- culties to the unified deployment of drought and flood control departments. [Conclu- sion] This study provided theoretical basis for the drought resistance, waterlogging prevention and disaster reduction in Weifang City under the background of climate change.

Using leaf area index(LAI) to assess vegetation response to drought in Yunnan province of China

Climatic extremes such as drought have becoming a severe climate-related problem in many regions all over the world that can induce anomalies in vegetation condition. Growth and CO2 uptake by plants are constrained to a large extent by drought.Therefore, it is important to understand the spatial and temporal responses of vegetation to drought across the various land cover types and different regions. Leaf area index(LAI) derived from Global Land Surface Satellite(GLASS) data was used to evaluate the response of vegetation to drought occurrence across Yunnan Province, China(2001-2010). The meteorological drought was assessed based on Standardized Precipitation Index(SPI)values. Pearson's correlation coefficients between LAI and SPI were examined across several timescales within six sub-regions of the Yunnan. Further, the drought-prone area was identified based on LAI anomaly values. Lag and cumulative effects of lack of precipitation on vegetation were evident, with significant correlations found using 3-, 6-, 9-and 12-month timescale. We found 9-month timescale has higher correlations compared to another timescale.Approximately 29.4% of Yunnan's area was classified as drought-prone area, based on the LAI anomaly values. Most of this drought-prone area was distributed in the mountainous region of Yunnan.From the research, it is evident that GLASS LAI can be effectively used as an indicator for assessing drought conditions and it provide valuable information for drought risk defense and preparedness.

Decadal Variations of Extreme Tropical Cyclones Influencing China during 1949-2009

Decadal variations of extreme tropical cyclones （TCs） influencing China were. investigated based on the tracks, landfall information, precipitation and wind data during 1949-2009. The extreme landfall date events are less in the 1970s and 2000s. The number of extreme events of maximum wind speed and minimum pressure near TC＇s center reached the highest in the 2000s. The extreme rain duration events had the highest frequence in the 1970s, and the extreme strong wind duration events had the maximum frequence in the 1980s. The number of stations whereat the extreme maximum daily precipitation or process precipitation is observed, is the largest in the 1960s, and the number of stations whereat daily maximum wind speed events axe observed, is the largest in the 1980s.

Urbanization effect on precipitation over the Pearl River Delta based on CMORPH data

Based on the satellite data from the Climate Prediction Center morphing(CMORPH) at very high spatial and temporal resolution, the effects of urbanization on precipitation were assessed over the Pearl River Delta(PRD) metropolitan regions of China. CMORPH data well estimates the precipitation features over the PRD. Compared to the surrounding rural areas, the PRD urban areas experience fewer and shorter precipitation events with a lower precipitation frequency(ratio of rainy hours, about 3 days per year less); however, short-duration heavy rain events play a more significant role over the PRD urban areas. Afternoon precipitation is much more pronounced over the PRD urban areas than the surrounding rural areas, which is probably because of the increase in short-duration heavy rain over urban areas.