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1.
基于安徽省81个气象站1961—2017年逐日降水数据及土壤墒情和干旱灾情资料,从诊断干旱日数年际变化、季节演变、空间分布、频率分布、典型干旱过程演变及与土壤墒情、干旱灾情的相关性等方面,研究6种时间尺度SPI在安徽省气象干旱监测效果。结果表明:不同时间尺度SPI在干旱监测中差异明显,6种时间尺度SPI对于干旱日数年际变化、不同等级干旱频率分布具有较好的监测效果,但对于干旱日数季节演变和空间差异性诊断与实况存在偏差;从典型干旱过程诊断来看,时间尺度越短,降水权重越大(例如SPI30、SPI60),SPI监测曲线对降水的响应越敏感,而SPI150、SPI180等时间尺度长的SPI对降水的响应又过于"迟钝";从与土壤墒情的相关性来看,时间尺度短的SPI30与10 cm表层土壤墒情相关性最好,相关系数达0.91,时间尺度长的SPI180与50 cm深层土壤墒情相关性较好;在各时间尺度SPI与年降水量的负相关及与干旱灾情的正相关方面,相关系数随着时间尺度的增长均先增后减,时间尺度适中的SPI120相关性最好。总体来看,不同时间尺度SPI代表不同含义,针对不同时间尺度的气象干旱应采用不同时间尺度的SPI进行监测评估。 相似文献
2.
近20年华北地区土壤水储量变化趋势及水分管理与调配对策 总被引：7，自引：1，他引：6
从35个台站土壤湿度实测资料出发,探讨了近20年华北地区土壤水储量变化趋势及时空特征。结果表明:全区年平均0~50 cm土壤水储量总体呈减少趋势,但区域差异明显。土壤变干最显著的两个中心区域分别为京津塘地区和山西西部,次显著中心为内蒙古东部。在0~50 cm深度范围内,从地表面开始,随深度增加,土壤水储量的减少幅度逐渐增加,且季节特征明显,即春秋季减少幅度大于夏冬季。各分区土壤水储量的变化趋势呈现出显著的年代际特征,就0~50 cm土壤水储量而言,各分区存在一个共同特点:1995~2002年均呈明显的波动下降变化趋势。土壤变干的趋势,对华北地区农业和生态具有一定的不利影响,因此结合区域实际提出相应的水分管理与调配措施。 相似文献
3.
NCEP/GFS analysis is used to investigate the scale dependence and the interplay between the terms of the atmospheric water
budget over West Africa using a dedicated decomposition methodology. The focus is on a 2-month period within the active monsoon
period of 2006. Results show that the dominant scales of seasonal mean precipitation and moisture flux divergence over West
Africa during the monsoon period are large scales (greater than 1,400 km) except over topography, where mean values of small
scales (smaller than 900 km) are strong. Correlations between moisture flux divergences in monsoon and African Easterly Jet
layers and precipitation indicate that precipitation is strongly correlated to moisture flux divergence via both large-scale
and small-scale processes, but the correlation signal is quite different depending on the region and vertical layer considered.
The analysis of the scales associated with the rainfall and the local evaporation over 3 different regions shows that positive
correlation exists over the ocean between precipitation and evaporation especially at large scale. Over the continent south
of the Sahel, the correlation is negative and driven by large scale. Over the northern part of Sahel, positive correlation
is found, only at small scales during the active monsoon period. Lag correlation reveals that the maximum evaporation over
the Sahel occurs 1–3 days after the maximum precipitation with maximum contribution from small-scale processes during the
first day. This study shows that NCEP/GFS reproduces well the known atmospheric water budget features. It also reveals a new
scale dependence of the relative role of each term of the atmospheric water budget. This indicates that such scale decomposition
approach is helpful to clarify the functioning of the water cycle embedded in the monsoon system. 相似文献
4.
Water stored as part of the land surface is lost to evapotranspiration and runoff on different time scales,and the partitioning between these time scales is important for modeling soil water in a climate model.Different time scales are imposed on evapotranspiration primarily because it is derived from different reservoirs with different storage capacities, from the very rapid evaporation of canopy stores to the slow removal by transpiration of rooting zone soil moisture. Runoff likewise ranges in time scale from rapid surface terms to the slower base-flow. The longest time scale losses of water determine the slow variation of soil moisture and hence the longer time scale effects of soil moisture on precipitation. This paper shows with a simple analysis how shifting the partitioning of evapotranspiration between the different reservoirs affects the variability of soil moisture and precipitation. In particular, it is concluded that a shift to shorter time scale reservoirs shifts the variance of precipitation from that which is potentially predictable to unpredictable. 相似文献
5.
利用GLDAS资料分析黄土高原半干旱区土壤湿度对气候变化的响应 总被引：1，自引：0，他引：1
利用GLDAS资料分析了1948~2010年黄土高原半干旱区气温、降水和土壤湿度的变化趋势,并重点讨论了气温和降水对土壤湿度的影响和相对贡献。结果表明:近60 a来黄土高原半干旱区整体呈现暖干化趋势,增温速率明显高于全球平均增温速率;不同深度的土壤湿度的长期变化均呈减小趋势,且年际间变化明显。不同深度的土壤湿度和气温呈负相关关系,并随着土壤加深,两者的相关性加强;土壤湿度和降水则呈正相关关系,相关关系最大出现在表层土壤。通过分析气温和降水在不同季节对土壤湿度的相对贡献发现,春季和冬季气温对土壤湿度的相对贡献较降水显著,秋季恰好相反,夏季气温和降水对土壤湿度的相对贡献大小相当。对比不同深度层降水、气温对土壤湿度的相对贡献得出,降水对浅层土壤湿度有显著作用,而气温对深层土壤湿度的作用更明显。 相似文献
6.
Through an Australia-China climate change bilateral project, we analyzed results of 51-year global offline simulations over China using the Australian community atmosphere biosphere land exchange (CABLE) model, focusing on integrated studies of its surface energy, water and carbon cycle at seasonal, interannual and longer time-scales. In addition to the similar features in surface climatology between the CABLE simulation and those derived from the global land-surface data assimilation system, comparison of surface fluxes at a CEOP reference site in northeast China also suggested that the seasonal cycles of surface evaporation and CO2 flux are reasonably simulated by the model. We further assessed temporal variations of model soil moisture with the observed variations at a number of locations in China. Observations show a soil moisture recharge–discharge mechanism on a seasonal time scale in central-east China, with soil moisture being recharged during its summer wet season, retained in its winter due to low evaporation demand, and depleted during early spring when the land warms up. Such a seasonal cycle is shown at both 50- and 100-cm soil depths in observations while the model only shows a similar feature in its lower soil layers with its upper layer soil moisture varying tightly with rainfall seasonal cycle. In the analysis of the model carbon cycle, the net primary productivity (NPP) has similar spatial patterns as the ones derived from an ecosystem model with remote sensing. The simulated interannual variations of NPP by CABLE are consistent with the results derived from remote sensing-based and process-based studies over the period of 1981–2000. Nevertheless an upward trend from observations is not presented in the model results. The model shows a downward trend primarily due to the constant CO2 concentration used in the experiment and a large increase of autotrophic respiration caused by an upward trend in surface temperature forcing data. Furthermore, we have compared river discharge data from the model experiments with observations in the Yangtze and Yellow River basins in China. In the Yangtze River basin, while the observed interannual variability is reasonably captured, the model significantly underestimates its river discharge, which is consist with its overestimation of evaporation in the region. In the Yellow River basin, the magnitudes of the river discharge is similar between modeled and observed but its variations are less skillfully captured as seen in the Yangtze River region. 相似文献
7.
采用2004年Casati提出的强度-尺度检验技术,选取2008年汛期代表不同类型降水(对流云降水、层状云降水、混合云降水)的4个降水过程,从尺度分解角度入手,对"世界气象组织天气研究计划——北京奥运会预报示范项目"(WWRP B08FDP)项目中4个I临近预报参加系统(BJANC,GRAPES-SWIFT,STEPS,CARDS)的1h定量降水预报进行时空尺度分解检验,研究降水预报技巧与降水时空尺度和强度之间的关系。结果表明:尽管目前国际先进的临近预报系统的水平分辨率已高达1～2km,但其有技巧的临近预报能力主要集中于空间尺度大于32km、时间尺度大于1h的降水系统,而对小于这些尺度的降水系统预报能力仍非常有限;在不同时空尺度的临近预报降水误差中,60%以上的误差来自于空间尺度小于8km的降水,85%以上的误差来自于时间尺度小于1h的降水,传统的外推技术不能满足这些较小时空尺度降水预报的需求,要发展有效的预报方法来提高较小时空尺度降水的预报能力。将基于外推的临近预报和基于稠密观测资料、快速更新的数值预报的潜势预报相结合可能是一条有效的解决途径。 相似文献
8.
本文利用1981～2016年的CRUNCEP资料（0.5°×0.5°）作为大气驱动数据,驱动CLM4.5（Community Land Model version 4.5）模式模拟了青藏高原地区1981～2016 年的土壤湿度时空变化。将模拟数据与台站观测资料、再分析资料（ERA-Interim和GLDAS-CLM）和微波遥感FY-3B/MWRI土壤湿度资料对比验证,表明了CLM4.5模拟资料可以合理再现青藏高原地区土壤湿度的空间分布和长期变化趋势。而且基于多种卫星遥感资料建立的较高分辨率（0.1°×0.1°）的青藏高原地表数据更加细致地刻画了土壤湿度的空间变化。对比结果表明:CLM4.5模拟土壤湿度与各个台站观测的时空变化一致,各层土壤湿度的模拟和观测均显著相关,且对浅层的模拟优于深层,但模拟结果比台站观测系统性偏大。模拟与再分析资料和微波遥感资料土壤湿度的空间分布具有一致性,均表现为从青藏高原的西北部向东南部逐渐增加的分布特点,三江源湿地和高原东南部为土壤湿度的高值区,柴达木盆地和新疆塔里木盆地的沙漠地区为低值区,土壤湿度由浅层向深层增加。土壤湿度的长期变化趋势基本表现为“变干—变湿”相间的带状分布,不同层次的土壤湿度变化趋势基本一致。模拟资料也合理地再现了夏季土壤湿度逐月的变化:高原西南地区的土壤湿度明显大范围增加,北部的柴达木盆地的干旱范围也明显的向北收缩,高原南部外围土壤湿度也明显增加,CLM4.5模拟土壤湿度比再分析资料和微波遥感资料更加细致地描述了夏季逐月土壤湿度空间分布及其变化特征。 相似文献
9.
基于气候系统内在层次性的气象干旱指数研究 总被引：3，自引：1，他引：2
气候系统除了具有非线性/非平稳性,还有层次性,许多大小不一的时空尺度构成了多层次结构,不同层次的气候系统具有不同的可预报性和稳定性。对于一种气象干旱指数而言,主要考虑从某一时段(尺度)内降水、温度、土壤湿度等要素测量值来建立干旱指数。本文首先从气候系统的非线性/非平稳性和内在层次性出发,针对中国不同地区的区域气候及其变化特征,使用信息熵方法从降水观测资料中提取出区域降水的两个(均态和变化)本征尺度,提出一种基于区域气候系统层次性内在特征的气象干旱指数MSPI。以2011年长江中下游春季严重气象干旱的发生、发展、持续、缓解情况为例,对MSPI的干旱监测能力进行检验。发现MSPI对不同程度的干旱都有较好的表征能力,并且对于干旱过程也有较好的识别能力。从各方面综合考虑,MSPI是一种可以较好满足逐日气象干旱监测、检测需求的气象干旱指数。在实际应用中,气象干旱指数MSPI可以作为其他不同时间尺度上的各种干旱指数的有益补充。 相似文献
10.
Yetang Wang Harald Sodemann Shugui Hou Valérie Masson-Delmotte Jean Jouzel Hongxi Pang 《Climate Dynamics》2013,40(3-4):731-742
The spatial and temporal variability of snow accumulation near Dome Argus, Antarctica, is assessed using new snow pit and stake measurement data together with existing snow pit, ice core and automatic weather station records. Snow accumulation rate shows large inter-annual variations, but stable multi-decadal levels over the last seven centuries. Spatial variations in snow accumulation within the space of 50 km of Dome Argus are relatively small, probably thanks to the smooth topography. A comparison of theses accumulation observations with ECMWF reanalyses (ERA-40 and ERA-Interim) suggests ECMWF reanalysis captures the seasonal variations, but underestimates the overall snow accumulation at Dome Argus by ~50 %. The moisture sources for precipitation over Dome Argus are examined by means of a Lagrangian moisture source diagnostic, based on the tracing of specific humidity changes along air parcel trajectories, for the period 2000–2004 using operational ECMWF analysis data. Dome Argus mainly receives moisture from the mid-latitude (46 ± 4°S) South Indian Ocean, with a seasonal latitudinal shift of about 6°. Compared to other central East Antarctic deep ice core sites such as Dome F, Dome C, Vostok, and EPICA Dronning Maud Land, Dome Argus has a more southerly moisture origin, probably due to topographic influences on the moisture transport paths. These results have important implications for the interpretation of future ice cores at Dome Argus. 相似文献
11.
本文首先利用中国气象局国家气象信息中心提供的中国732个站点观测的土壤体积含水量,评估了CLM4.5（Community Land Model version 4.5）在CFSR（Climate Forecast System Reanalysis）近地面大气数据驱动下模拟的逐月土壤湿度（记为CLM4.5-CFSR）,然后基于CLM4.5-CFSR比较了皮尔逊相关法和自相关法计算得到的1980～2009年中国地区土壤湿度记忆性的区域及季节分布特征,量化了土壤湿度的记忆能力,研究了降水频率、降水强度和近地表气温分别对土壤湿度记忆性的影响。结果表明:CLM4.5-CFSR能较好地反映出大部分地区月时间尺度上土壤湿度的变化特征。两种方法描述的土壤湿度记忆性的空间分布特征相似,但季节特征不同。不同深度土壤湿度的记忆时长相差不大,在0.85～2.2个月不等,其中内蒙古东北部较大,新疆西南部较小。春季,较湿的土壤记忆性也较强。当降水频率较低时,其对蒸发速率较大的地区土壤湿度的记忆性影响很小,当降水强度较大时,它会迅速补充土壤散失的水分,破坏初始时刻土壤的干湿状态,引起其记忆性减弱。近地表气温变化主要通过影响土壤的蒸发过程减弱土壤湿度的记忆性。未来可利用气候模式开展数值敏感性试验对本文得到的结论进行机理研究,为进一步提高季节和季节内尺度的降水预报提供依据。 相似文献
12.
Yoshimitsu Masaki Yasushi Ishigooka Tsuneo Kuwagata Shinkichi Goto Shinji Sawano Toshihiro Hasegawa 《Theoretical and Applied Climatology》2011,106(3-4):383-401
We have studied future changes in the atmospheric and hydrological environments in Northeast Thailand from the viewpoint of risk assessment of future cultural environments in crop fields. To obtain robust and reliable estimation for future climate, ten general circulation models under three warming scenarios, B1, A1B, and A2, were used in this study. The obtained change trends show that daily maximum air temperature and precipitation will increase by 2.6°C and 4.0%, respectively, whereas soil moisture will decrease by c.a. 1% point in volumetric water content at the end of this century under the A1B scenario. Seasonal contrasts in precipitation will intensify: precipitation increases in the rainy season and precipitation decreases in the dry season. Soil moisture will slightly decrease almost throughout the year. Despite a homogeneous increase in the air temperature over Northeast Thailand, a future decrease in soil water content will show a geographically inhomogeneous distribution: Soil will experience a relative larger decrease in wetness at a shallow depth on the Khorat plateau than in the surrounding mountainous area, reflecting vegetation cover and soil texture. The predicted increase in air temperature is relatively consistent between general circulation models. In contrast, relatively large intermodel differences in precipitation, especially in long-term trends, produce unwanted bias errors in the estimation of other hydrological elements, such as soil moisture and evaporation, and cause uncertainties in projection of the agro-climatological environment. Offline hydrological simulation with a wide precipitation range is one strategy to compensate for such uncertainties and to obtain reliable risk assessment of future cultural conditions in rainfed paddy fields in Northeast Thailand. 相似文献
13.
1. Introduction The soil moisture plays an important role in in- fluencing the climate change by altering the surface albedo, soil heat capacity and the heat flux between air and land (Ma et al., 2001). Near-surface soil mois- ture controls the partitioni… 相似文献
14.
Kun Yang Baisheng Ye Degang Zhou Bingyi Wu Thomas Foken Jun Qin Zhaoye Zhou 《Climatic change》2011,109(3-4):517-534
The Tibetan Plateau (TP) surfaces have been experiencing an overall rapid warming and wetting while wind speed and solar radiation have been declining in the last three decades. This study investigated how climate changes influenced the hydrological cycle on the TP during 1984??2006. To facilitate the analysis, a land surface model was used to simulate surface water budget at all CMA (China Meteorological Administration) stations on the TP. The simulated results were first validated against observed ground temperature and observation-derived heat flux on the western TP and observed discharge trends on the eastern TP. The response of evaporation and runoff to the climate changes was then analyzed. Major finding are as follows. (1) Surface water balance has been changed in recent decades. Observed precipitation shows insignificant increasing trends in central TP and decreasing trends along the TP periphery while evaporation shows overall increasing trends, leading to decreased discharge at major TP water resource areas (semi-humid and humid zones in the eastern and southern TP). (2) At the annual scale, evaporation is water-limited in dry areas and energy-limited (radiation and air temperature) in wet areas; these constraints can be interpreted by the Budyko-curve. Evaporation in autumns and winters was strongly controlled by soil water storage in summers, weakening the dependence of evaporation on precipitation at seasonal scales. (3) There is a complementary effect between the simulated actual evaporation and potential evaporation, but this complementary relationship may deviate from Bouchet??s hypothesis when vapor pressure deficit (or air temperature) is too low, which suppresses the power of vapor transfer. 相似文献
15.
依据国家沈阳农田生态系统野外研究站2006-2010年监测数据,分析0-100cm 土层8个层次的地温、0-100 cm地温、地温极值、0-20 cm地温与气温的关系和土壤热通量的变化趋势。结果表明：从年际变化看,8个层次地温和地温极值呈下降趋势;0 cm层次地温变化受外界影响较大。研究区域年尺度0-20 cm地温与气温有比较一致的变化规律。作物生长季节,可分为4-7月气温上升和8-10月气温下降两阶段;这两个不同阶段的0-20 cm地温与气温分别做线性拟合,与整个生长季4-10月线性拟合相比,线性相关性可信度更高。土壤热通量受气温和土壤质量含水量影响年际变化较大,年尺度土壤热通量≥0 MJ/m2,该区域地表是热汇。 相似文献
16.
有效降水对于土壤水分的补充和农作物的生长来说是一个很重要的概念。通常认为大于5 mm的降水即为有效降水。但是有效降水的影响因素很多,在不同的地理环境和气候背景条件下,最小有效降水量也会有所不同。利用2006年6月—2011年3月兰州大学半干旱气候与环境观测站资料,从土壤湿度变化的角度出发,根据有效降水的定义,对甘肃榆中地区的最小有效降水量做了初步研究。通过分析该地区不同季节、温度和植被条件下不同土壤深度最小有效降水量,发现5、10、20 cm土壤层的最小有效降水量分别为4、5、8 mm。季节分布上,各层土壤最小有效降水量均为夏季最高,春季和秋季值较为接近。高温年的最小有效降水量高于低温年的值,生长季高于非生长季。在降水超过最小有效降水量并且量级较小时,随着降水量的增大,土壤湿度增量呈指数形式增大,这时降水的转化率也较高;而当降水达到一定量级时,超过了土壤的入渗率,水分以径流的形式损失,土壤湿度增量的变化率减小,降水的转化率也趋于一定值。0—20 cm土壤层降水转化率达到70%。 相似文献
17.
Moisture Sources and Their Contributions to Summer Precipitation in the East of Southwest China 
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下载免费PDF全文 Complex topography, special geographical location and sea-land-air interactions lead to high interannual variability of summer precipitation in the east of Southwest China (ESWC). However, the contributions, influencing factors and mechanisms of remote and local evaporation remain to be further investigated. Using clustering analysis and Hybrid Single-Particle Lagrangian Integrated Trajectory version 5 model, we analyze the contributions of remote moisture transport and local evaporation to summer precipitation in the ESWC and their causes. There are mainly five remote moisture channels in the ESWC, namely the Arabian Sea channel, Bay of Bengal channel, western Pacific channel, Northwest channel 1 and Northwest channel 2. Among the five channels, the western Pacific channel has the largest number of trajectories, while the Bay of Bengal channel has the largest contribution rate of specific humidity (33.33%) and moisture flux (33.14%). The amount of regional average precipitation is close to that of the precipitation caused by remote moisture transport, and both are considerably greater than the rainfall amount caused by local evaporation. However, on interannual time scales, precipitation recirculation rates are negatively correlated to regional average precipitation and precipitation caused by remote moisture transport but are consistent with that caused by local evaporation. An apparent "+ ? +" wave train can be found on the height anomaly field in East Asia, and the sea surface temperature anomalies are positive in the equatorial Middle-East Pacific, the South China Sea, the Bay of Bengal and the Arabian Sea. These phenomena cause southwest-northeast moisture transport with strong updrafts, thereby resulting in more precipitation in the ESWC. 相似文献
18.
Spatiotemporal patterns of drought at various time scales in Shandong Province of Eastern China 总被引：1，自引：0，他引：1
The temporal variations and spatial patterns of drought in Shandong Province of Eastern China were investigated by calculating the standardized precipitation evapotranspiration index (SPEI) at 1-, 3-, 6-, 12-, and 24-month time scales. Monthly precipitation and air temperature time series during the period 1960–2012 were collected at 23 meteorological stations uniformly distributed over the region. The non-parametric Mann-Kendall test was used to explore the temporal trends of precipitation, air temperature, and the SPEI drought index. S-mode principal component analysis (PCA) was applied to identify the spatial patterns of drought. The results showed that an insignificant decreasing trend in annual total precipitation was detected at most stations, a significant increase of annual average air temperature occurred at all the 23 stations, and a significant decreasing trend in the SPEI was mainly detected at the coastal stations for all the time scales. The frequency of occurrence of extreme and severe drought at different time scales generally increased with decades; higher frequency and larger affected area of extreme and severe droughts occurred as the time scale increased, especially for the northwest of Shandong Province and Jiaodong peninsular. The spatial pattern of drought for SPEI-1 contains three regions: eastern Jiaodong Peninsular and northwestern and southern Shandong. As the time scale increased to 3, 6, and 12 months, the order of the three regions was transformed into another as northwestern Shandong, eastern Jiaodong Peninsular, and southern Shandong. For SPEI-24, the location identified by REOF1 was slightly shifted from northwestern Shandong to western Shandong, and REOF2 and REOF3 identified another two weak patterns in the south edge and north edge of Jiaodong Peninsular, respectively. The potential causes of drought and the impact of drought on agriculture in the study area have also been discussed. The temporal variations and spatial patterns of drought obtained in this study provide valuable information for water resources planning and drought disaster prevention and mitigation in Eastern China. 相似文献
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Jianxiu Qiu Xingguo Mo Suxia Liu Zhonghui Lin 《Theoretical and Applied Climatology》2014,118(1-2):159-171
Soil moisture variability of various spatial scales is analyzed based on empirical orthogonal function (EOF) method using soil moisture datasets with various spatial resolutions: 1 km eco-hydrological model simulation, 0.25° passive microwave (Advanced Microwave Scanning Radiometer for the Earth Observing System, AMSR-E) dataset, and 0.5° land surface model simulation from Climate Predictor Center (CPC). All three datasets generate EOFs that explain similar variances with those generated from in situ observations from agro-meteorological network. Using AMSR-E product and eco-hydrological model simulation, it is found that the primary spatial pattern of soil moisture obtained from watershed scale has a strong connection to topographic attributes, followed by soil texture and rainfall variability, as suggested by the correlation between the primary EOF mode (EOF1) of soil moisture and landscape attributes. However, the EOF analysis of both AMSR-E and CPC datasets at regional scale reaches the conclusion that soil texture indices, such as sand and clay content, is of higher importance to soil moisture EOF1 spatial pattern (explaining 61 % variance) than topography is. Furthermore, correlation between soil moisture EOF1 and soil property is higher in spring than in autumn, which indicates that soil water-holding and drainage capabilities are more important under dry conditions. At national scale, the combined effects of topographic feature and soil property are clearly exhibited in EOF1. The study results reveal that different emphases should be placed on accurate acquisition of landscape attributes for soil moisture estimation according to various spatial scales. 相似文献
20.
Atmospheric Moisture Residence Times and Cycling: Implications for Rainfall Rates and Climate Change 总被引：16，自引：0，他引：16
Kevin E. Trenberth 《Climatic change》1998,39(4):667-694
New estimates of the moistening of the atmosphere through evaporation at the surface and of the drying through precipitation are computed. Overall, the e-folding residence time of atmospheric moisture is just over 8 days. New estimates are also made of how much moisture that precipitates out comes from horizontal transport versus local evaporation, referred to as recycling. The results depend greatly on the scale of the domain under consideration and global maps of the recycling for annual means are produced for 500 km scales for which global recycling is 9.6%, consisting of 8.9% over land and 9.9% over the oceans. Even for 1000 km scales, less than 20% of the annual precipitation typically comes from evaporation within the domain. While average overall atmospheric moisture depletion and restoration must balance, precipitation falls only a small fraction of the time. Thus precipitation rates are also examined. Over the United States, one hour intervals with 0.1 mm or more are used to show that the frequency of precipitation ranges from over 30% in the Northwest, to about 20% in the Southeast and less than 4% just east of the continental divide in winter, and from less than 2% in California to over 20% in the Southeast in summer. In midlatitudes precipitation typically falls about 10% of the time, and so rainfall rates, conditional on when rain is falling, are much larger than evaporation rates. The mismatches in the rates of rainfall versus evaporation imply that precipitating systems of all kinds feed mostly on the moisture already in the atmosphere. Over North America, much of the precipitation originates from moisture advected from the Gulf of Mexico and subtropical Atlantic or Pacific a day or so earlier. Increases in greenhouse gases in the atmosphere produce global warming through an increase in downwelling infrared radiation, and thus not only increase surface temperatures but also enhance the hydrological cycle, as much of the heating at the surface goes into evaporating surface moisture. Global temperature increases signify that the water-holding capacity of the atmosphere increases and, together with enhanced evaporation, this means that the actual atmospheric moisture should increase. It follows that naturally-occurring droughts are likely to be exacerbated by enhanced potential evapotranspiration. Further, globally there must be an increase in precipitation to balance the enhanced evaporation but the processes by which precipitation is altered locally are not well understood. Observations confirm that atmospheric moisture is increasing in many places, for example at a rate of about 5% per decade over the United States. Based on the above results, we argue that increased moisture content of the atmosphere therefore favors stronger rainfall or snowfall events, thus increasing risk of flooding, which is a pattern observed to be happening in many parts of the world. Moreover, because there is a disparity between the rates of increase of atmospheric moisture and precipitation, there are implied changes in the frequency of precipitation and/or efficiency of precipitation (related to how much moisture is left behind in a storm). However, an analysis of linear trends in the frequency of precipitation events for the United States corresponding to thresholds of 0.1 and 1 mm/h shows that the most notable statistically significant trends are for increases in the southern United States in winter and decreases in the Pacific Northwest from November through January, which may be related to changes in atmospheric circulation and storm tracks associated with El Niño–Southern Oscillation trends. It is suggested that as the physical constraints on precipitation apply only globally, more attention should be paid to rates in both observations and models as well as the frequency of occurrence. 相似文献