Changes In Precipitation Frequency Research Articles

Non-uniform changes of daily precipitation in China: Observations and simulations

Daily precipitation of different intensities is expected to change differently in response to global warming. Based on station observations and simulations from the latest climate models, we investigated the non-uniform features of changes in daily precipitation frequency, intensity and amount over China. Results show that western China experiences an overall wetting trend across the spectrum of precipitation intensity, while eastern China exhibits negative trends in light-to-moderate precipitation and positive trends in heavy-to-extreme precipitation with respect to precipitation frequency and amount. Changes in precipitation intensity do not show a spatially consistent pattern of intensification in most intensity spectra, but exhibit the most pronounced intensification in heavy-to-extreme precipitation. Interestingly, changes in precipitation frequency dominate changes in the amount of precipitation for each intensity level, particularly for the spatial patterns. Although climate models show limited skills in reproducing the magnitudes of these observed changes, they show skills in simulating the sign of the changes. Also, they reasonably reproduce the observed non-uniform patterns of daily precipitation changes, especially for changes in the contributions from different intensity levels to annual total precipitation on average over the whole country. The evaluation of current climate models in simulating daily precipitation changes as a function of precipitation intensity suggests that improvement in the detection and attribution of precipitation changes in China can be gained by dividing daily precipitation into different categories.

Predicting extreme sub-hourly precipitation intensification based on temperature shifts

Abstract. Extreme sub-hourly precipitation, typically convective in nature, is capable of triggering natural disasters such as floods and debris flows. A key component of climate change adaptation and resilience is quantifying the likelihood that sub-hourly extreme precipitation will exceed historical levels in future climate scenarios. Despite this, current approaches to estimating future sub-hourly extreme precipitation return levels are deemed insufficient. The reason for this can be attributed to two factors: there is limited availability of data from convection-permitting climate models (capable of simulating sub-hourly precipitation adequately) and the statistical methods we use to extrapolate extreme precipitation return levels do not capture the physics governing global warming. We present a novel physical-based statistical method for estimating the extreme sub-hourly precipitation return levels. The proposed model, named TEmperature-dependent Non-Asymptotic statistical model for eXtreme return levels (TENAX), is based on a parsimonious non-stationary and non-asymptotic theoretical framework that incorporates temperature as a covariate in a physically consistent manner. We first explain the theory and present the TENAX model. Using data from several stations in Switzerland as a case study, we demonstrate the model's ability to reproduce sub-hourly precipitation return levels and some observed properties of extreme precipitation. We then illustrate how the model can be utilized to project changes in extreme sub-hourly precipitation in a future warmer climate only based on climate model projections of temperatures during wet days and on foreseen changes in precipitation frequency. We conclude by discussing the uncertainties associated with the model, its limitations, and its advantages. With the TENAX model, one can project sub-hourly precipitation extremes at different return levels based on daily scale projections from climate models in any location globally where observations of sub-hourly precipitation data and near-surface air temperature are available.

Increased erosion in a pre-Alpine region contrasts with a future decrease in precipitation and snowmelt

Climate change is affecting the hydromorphological system. In many places, changes in sediment dynamics are closely correlated to changes in precipitation frequency and magnitude. However, in nivo-pluvial regimes, the hydromorphological response to climate is more challenging to predict as it is not only the amount and occurrence of precipitation that is changing. The changes in precipitation type (i.e., snow or rain), snow accumulation, and snowmelt rates will also have a significant effect on the catchment net precipitation (composed of direct precipitation plus snowmelt contribution), and this may affect overland flow, erosion, stream discharge, sediment transport, and deposition. We investigated the impacts of climate change on hydrology and geomorphology in a small catchment (Emme, 127 km2) located in the Swiss pre-Alps by simulating the difference between the hydromorphological response to net precipitation in the present climate and in three climate scenarios at the end of the century using the CAESAR-Lisflood landscape evolution model. For the most extreme climate scenario (RCP8.5), simulations showed that despite the reduction in net precipitation (by 7 %) and discharge (by 4 %), sediment yield at the outlet of the catchment increased by 6 %. This is not only because precipitation falls more as rain than snow during the cold months, but also because heavy precipitation is expected to intensify. On a seasonal scale, we found that the amount of net precipitation, discharge, and erosion will increase in winter at the end of the century, while it will decrease in spring. In all three climate scenarios, net precipitation is projected to decrease in summer, but sediment yields may both decrease or increase. Autumn is the season with the greatest changes in erosion, while net precipitation remains constant or only slightly increases. Furthermore, we found that erosion and deposition patterns are changing spatially, with more erosion in mid-elevations and more deposition in valleys. Although our results are specific to the study site, we expect similar trends in other catchments of the pre-Alpine region.

Significant effects of precipitation frequency on soil respiration and its components-A global synthesis.

Global warming intensifies the hydrological cycle, which results in changes in precipitation regime (frequency and amount), and will likely have significant impacts on soil respiration (Rs ). Although the responses of Rs to changes in precipitation amount have been extensively studied, there is little consensus on how Rs will be affected by changes in precipitation frequency (PF) across the globe. Here, we synthesized the field observations from 296 published papers to quantify the effects of PF on Rs and its components using meta-analysis. Our results indicated that the effects of PF on Rs decreased with an increase in background mean annual precipitation. When the data were grouped by climate conditions, increased PF showed positive effects on Rs under the arid condition but not under the semi-humid or humid conditions, whereas decreased PF suppressed Rs across all the climate conditions. The positive effects of increased PF mainly resulted from the positive response of heterotrophic respiration under the arid condition while the negative effects of decreased PF were mainly attributed to the reductions in root biomass and respiration. Overall, our global synthesis provided for the first time a comprehensive analysis of the divergent effects of PF on Rs and its components across climate regions. This study also provided a framework for understanding and modeling responses of ecosystem carbon cycling to global precipitation change.

Water Stress-Driven Changes in Bacterial Cell Surface Properties.

Increased drought intensity and frequency exposes soil bacteria to prolonged water stress. While numerous studies reported on behavioral and physiological mechanisms of bacterial adaptation to water stress, changes in bacterial cell surface properties during adaptation are not well researched. We studied adaptive changes in cell surface hydrophobicity (CSH) after exposure to osmotic (NaCl) and matric stress (polyethylene glycol 8000 [PEG 8000]) for six typical soil bacteria (Bacillus subtilis, Arthrobacter chlorophenolicus, Pseudomonas fluorescens, Novosphingobium aromaticivorans, Rhodococcus erythropolis, and Mycobacterium pallens) covering a wide range of cell surface properties. Additional physicochemical parameters (surface chemical composition, surface charge, cell size and stiffness) of B. subtilis and P. fluorescens were analyzed to understand their possible contribution to CSH development. Changes in CSH caused by osmotic and matric stress depend on strain and stress type. CSH of B. subtilis and P. fluorescens increased with stress intensity, R. erythropolis and M. pallens exhibited a generally high but constant contact angle, while the response of A. chlorophenolicus and N. aromaticivorans depended on growth conditions and stress type. Osmotically driven changes in CSH of B. subtilis and P. fluorescens are accompanied by increasing surface N/C ratio, suggesting an increase in protein concentration within the cell wall. Cell envelope proteins thus presumably control bacterial CSH in two ways: (i) by increases in the relative density of surface proteins due to efflux of cytoplasmic water and subsequent cell shrinkage, and (ii) by destabilization of cell wall proteins, resulting in conformational changes which render the surface more hydrophobic. IMPORTANCE Changes in precipitation frequency, intensity, and temporal distribution are projected to result in increased frequency and intensity of droughts and heavy rainfall events. Prolonged droughts can promote the development of soil water repellency (SWR); this impacts the infiltration and distribution of water in the soil profile, exposing soil microorganisms to water stress. Exposure to water stress has recently been reported to result in increased cell surface hydrophobicity. However, the mechanism of this development is poorly understood. This study investigates the changes in the physicochemical properties of bacterial cell surfaces under water stress as a possible mechanism of increased surface hydrophobicity. Our results improve understanding of the microbial response to water stress in terms of surface properties, the variations in stress response depending on cell wall composition, and its contribution to the development of SWR.

Present-day and future projection of East Asian summer monsoon in Coupled Model Intercomparison Project 6 simulations.

The East Asian summer monsoon (EASM) is an influential monsoon system that provides two-thirds of the annual precipitation in the Asian region. Therefore, considerable attention has been paid to the changes in future climate. Thus far, studies on EASM characteristics have not been conducted considering specific global warming level (GWL) using Coupled Model Inter-comparison Project 6 (CMIP6) simulations. We analyze the EASM characteristics in present-day (PD) and the changes in EASM corresponding to the projections at 1.5, 2.0, and 3.0°C GWLs. The newly released 30 CMIP6 models effectively captured the migration of the monsoon in PD with a pattern correlation coefficient of 0.91, which is an improvement over that reported in previous studies. As a result of the separate analysis of the P1 (first primary peak; 33–41 pentad) and P2 (from P1 to the withdrawal; 42–50 pentad) periods, a higher frequency of weak to moderate precipitation in P2 and a smaller amount of moderate to extreme precipitation in P1 are mainly occurred. The CMIP6 models project increasing precipitation of approximately 5.7%°C−1, 4.0%°C−1, and 3.9%°C−1 for the three GWLs, respectively, with longer durations (earlier onset and delayed termination). Under the three GWLs, the projected precipitation frequency decreases below 6 mm d−1 (76th percentile) and significant increases above 29 mm d−1 (97th percentile). These changes in precipitation frequency are associated with an increasing distribution of precipitation amount above 97th percentile. Additionally, these tendencies in P1 and P2 are similar to that of the total period, while the maximum changes occur in 3.0°C GWL. In particular, future changes in EASM accelerate with continuous warming and are mainly affected by enhanced extreme precipitation (above 97th percentile). Our findings are expected to provide information for the implementation of sustainable water management programs as a part of national climate policy.

Spatiotemporal variation of precipitation on a global scale from 1960 to 2016 in a new normalized daily precipitation dataset

AbstractIncreases in total and extreme precipitation have been investigated worldwide using limited spatiotemporal data based on surface observations and satellite remote sensing during recent decades. However, it remains unclear whether rain gauge daily precipitation records also show a significant increase in global precipitation. In this study, we first apply the transformed version of the penalized maximum F test (“transPMFred”) to homogenize daily precipitation (P) records from 10,629 stations around the world during 1960–2016 from a dataset (GHCN‐CMA) that combines the daily precipitation data from the Global Historical Climatology Network (GHCN‐Daily) dataset and the China Meteorological Administration (CMA), and then utilize the homogenized data to study the frequency of daily precipitation on a global scale. The results indicate that precipitation frequency exhibited significant increasing trends from 1960 to 2016 across most of the globe, except for East Asia. Moreover, the variability of global precipitation frequency was more pronounced in wet regions than dry regions, especially in North America, Europe and East Asia based multiple daily precipitation datasets. The regional average frequency for moderate (30th < P ≤ 60th percentile), heavy (60th < P ≤ 90th percentile) and very heavy (P > 90th percentile) precipitation increased in North America and Europe. Changes in precipitation frequency decreased for light (P ≤ 30th percentile) and moderate precipitation but increased for heavy and very heavy precipitation, which mainly occurs in dry regions of Australia. Moreover, precipitation frequency in wet and dry regions of East Asia showed opposite trends, with a decrease in wet regions and an increase in dry regions.

Precipitation Pattern Regulates Soil Carbon Flux Responses to Nitrogen Addition in a Temperate Forest

Changes in precipitation frequency and intensity are predicted to be more intense and frequent accompanying climate change and may have immediate or potentially prolonged effects on soil CO2 and CH4 fluxes. However, how soil CO2 and CH4 fluxes respond to change in precipitation patterns remains poorly understood, especially under nitrogen (N) addition. In this study, we investigated the fluxes of soil CO2 and CH4 during a two-year field experiment and the effects of long-time precipitation reduction (− 30% of through-fall), short-term precipitation pulse and change of snow thickness on their response to simulated N deposition (50 kg N hm−2 y−1). Soil CO2 flux was greater enhanced by N addition in the relatively wet growing season (2016) than in the relatively dry growing season (2017), whereas soil CH4 flux was more inhibited by N addition in the relatively wet growing season 2016 than in the relatively dry growing season 2017. However, reduced precipitation decreased the positive effect of N addition on soil CO2 flux in the relatively wet growing season 2016, while changing the direction of N addition effect in the relatively dry growing season 2017. These results suggested that the precipitation patterns in the growing season may affect soil CO2 and CH4 fluxes response to N addition. Furthermore, we found that short-term extreme precipitation and thickness of snow cover had a significantly positive effect on soil CH4 flux but had a significantly negative effect on soil CO2 flux. The extreme precipitation, that is, very heavy precipitation, reduced the response magnitudes of soil CO2 and CH4 fluxes to reduced precipitation within 3 days, compared to wet precipitation and heavy precipitation. Our results indicated the significant effects of precipitation pattern changes on responses of soil C flux to N deposition, which should be incorporated into the global-C-cycling models to improve the prediction and reduce the uncertainty of C-climate feedbacks.

Changes in Observed Daily Precipitation over Global Land Areas since 1950

AbstractEstimates of observed long-term changes in daily precipitation globally have been limited due to availability of high-quality observations. In this study, a new gridded dataset of daily precipitation, called Rainfall Estimates on a Gridded Network (REGEN) V1–2019, was used to perform an assessment of the climatic changes in precipitation at each global land location (except Antarctica). This study investigates changes in the number of wet days (≥1 mm) and the entire distribution of daily wet- and all-day records, in addition to trends in annual and seasonal totals from daily records, between 1950 and 2016. The main finding of this study is that precipitation has intensified across a majority of land areas globally throughout the wet-day distribution. This means that when it rains, light, moderate, or heavy wet-day precipitation has become more intense across most of the globe. Widespread increases in the frequency of wet days are observed across Asia and the United States, and widespread increases in the precipitation intensity are observed across Europe and Australia. Based on a comparison of spatial pattern of changes in frequency, intensity, and the distribution of daily totals, we propose that changes in light and moderate precipitation are characterized by changes in precipitation frequency, whereas changes in extreme precipitation are primarily characterized by intensity changes. Based on the uncertainty estimates from REGEN, this study highlights all results in the context of grids with high-quality observations.

Categorization of precipitation changes in China under 1.5 °C and 3 °C global warming using the bivariate joint distribution from a multi-model perspective

This study examines the changes in the intensity and frequency of precipitation in China from a multi‐model perspective on 20 statistically downscaled fine-scale climate projections and categorizes them into four distinct patterns in response to globally targeted warming (1.5 °C and 3 °C). In a multivariate setting, the asymmetric responses of frequency and intensity to different levels of warming can be considered jointly. This study focuses on relatively moderate precipitation to determine if the ensemble of a subset of climate models, which are selected based on the categorization, can provide a better interpretation of the changing patterns compared to that from the conventional unweighted ensemble mean. The results show that the spatial distribution of the predominant category and inter-model agreement are dependent mainly on the degree of warming. As warming becomes more extensive, the projected change in precipitation tends to converge to the category that indicates an increase in both the intensity and frequency of precipitation, from the mixed-mode and even decreasing pattern. The use of subsampling to produce an ensemble of joint probability (or return period) has potential benefits in detecting asymmetric changes in the intensity and frequency of precipitation that is seen in the majority of models but hidden by the unweighted ensemble average particularly for regions where different models show mixed signals. A substantial portion of the region in China is likely to experience a transition of changes in precipitation frequency and (or) intensity under continuous warming, which would not be revealed clearly by univariate analysis.

Response of herbaceous wetland plant species to changing precipitation regimes

AbstractThe structure of wetland plant communities is sensitive to patterns of precipitation. In some regions, climate change is expected to result in more large‐magnitude, infrequent precipitation events. Typically, the response of wetland plants to changing precipitation regimes is studied under alterations in the amount of precipitation (drought), rather than event frequency. Here, we seek to understand how changes in rainfall frequency affect (a) soil moisture variability, (b) plant performance, and (c) plant C and N concentrations. We conducted a greenhouse study using eight herbaceous plant species (three eudicots, five monocots) subject to three precipitation treatments: (a) 80 mm per month distributed in equal volumes every 3 days (control treatment), (b) 80 mm per month distributed every 15 days (infrequent treatment), and (c) 110 mm per month distributed every 15 days (large magnitude‐infrequent treatment). Infrequent treatments decreased soil moisture by >60% compared with the control. Rainfall frequency affected soil moisture losses to evapotranspiration, which differed between early‐ and late‐growing seasons. This soil moisture stress in the infrequent treatments contributed to a 10–49% decrease in biomass among all eudicot species and a 25–54% decrease in two monocots. In contrast, changes in C and N concentration were limited to two forb species. Our results show that changes in precipitation frequency can strongly impact some wetland species. For some impacted species increased magnitude can alleviate the negative effects of infrequent rainfall. These results provide insight into how forecasted changes in the frequency and magnitude of precipitation may affect wetland plant species.

Spatio‐temporal November and March snowfall trends in the Lake Michigan region

This study has investigated the spatio‐temporal variability of November and March Lake Michigan snowfall for the period 1950–2013. Snowfall characteristics were assessed using time series analysis, geographic information systems, and visualization. Results indicate significant temporal decreases of November and March snowfall, peak inter‐annual variability within the lake‐effect belt, modest concurrent and lagged sensitivity to teleconnection indices, and strong dependence of snowfall on temperature. The decreased snowfall is in contrast to December–February snowfall and associated with a decreasing fraction of November and March precipitation days occurring as snow days, rather than changes in precipitation frequency. The decreasing fraction of precipitation days occurs as snowfall is consistent with synoptic‐scale disturbances producing rain rather than snow and lake‐effect rain falling in lieu of snow.

Drought and Carbon Cycling of Grassland Ecosystems under Global Change: A Review

In recent years, the increased intensity and duration of droughts have dramatically altered the structure and function of grassland ecosystems, which have been forced to adapt to this change in climate. Combinations of global change drivers such as elevated atmospheric CO2 concentration, warming, nitrogen (N) deposition, grazing, and land-use change have influenced the impact that droughts have on grassland C cycling. This influence, to some extent, can modify the relationship between droughts and grassland carbon (C) cycling in the multi-factor world. Unfortunately, prior reviews have been primarily anecdotal from the 1930s to the 2010s. We investigated the current state of the study on the interactive impacts of multiple factors under drought scenarios in grassland C cycling and provided scientific advice for dealing with droughts and managing grassland C cycling in a multi-factor world. Currently, adequate information is not available on the interaction between droughts and global change drivers, which would advance our understanding of grassland C cycling responses. It was determined that future experiments and models should specifically test how droughts regulate grassland C cycling under global changes. Previous multi-factor experiments of current and future global change conditions have studied various drought scenarios poorly, including changes in precipitation frequency and amplitude, timing, and interactions with other global change drivers. Multi-factor experiments have contributed to quantifying these potential changes and have provided important information on how water affects ecosystem processes under global change. There is an urgent need to establish a systematic framework that can assess ecosystem dynamic responses to droughts under current and future global change and human activity, with a focus on the combined effects of droughts, global change drivers, and the corresponding hierarchical responses of an ecosystem.

Impacts of warming and changes in precipitation frequency on the regeneration of two Acer species

Climate projections indicate that temperatures will increase by up to 4.5°C in Europe by the end of this century, and that more extreme rainfall events and longer intervening dry periods will take place. Climate change will likely affect all phases of the life cycle of plants, but plant reproduction has been suggested to be especially sensitive. Here, using a combination of approaches (soil heaters and different provenances along a latitudinal gradient), we analyzed the regeneration from seeds of Acer platanoides and A. pseudoplatanus, two tree species considered, from a management point of view, of secondary relevance. We studied germination, seedling survival and growth in a full-factorial experiment including warming and changes in watering frequency. Both species responded to warming, watering frequency and seed provenance, with stronger (negative) effects of warming and provenance than of watering frequency. In general, the central provenances performed better than the northernmost and southernmost provenances. We also detected interactive effects between warming, watering frequency and/or seed provenance. Based on these results, both species are expected to show dissimilar responses to the changes in the studied climatic factors, but also the impacts of climate change on the different phases of plant regeneration may differ in direction and magnitude. In general increases in the precipitation, frequency will stimulate germination while warming will reduce survival and growth. Moreover, the frequent divergent responses of seedlings along the latitudinal gradient suggest that climate change will likely have heterogeneous impacts across Europe, with stronger impacts in the northern and southern parts of the species’ distribution ranges.

The dominant role of heavy precipitation in precipitation change despite opposite trends in west and east of northern China

ABSTRACTBased on daily precipitation measurements from 271 meteorological stations in northern China during 1960–2011, we found that precipitation amount did not show significant trend (p = 0.25). To obtain a better understanding of regional precipitation differences, we divided northern China into two regions and five sub‐regions. A wetting tendency was identified for the northwestern of China (NW), while a drying tendency was determined for the northeastern of China (NE). Precipitation tendencies also displayed regional differences. We determined that changes in precipitation frequency dominated changes in precipitation amount for low altitude areas, while changes in precipitation intensity were the main cause of changes in precipitation amount in high altitude areas. Both precipitation frequency and intensity had an equivalent impact on changes within middle altitude regions of the NW. In contrast, changes in precipitation amount within the NE were mainly caused by precipitation frequency. The effect of precipitation intensity on precipitation amount was not significant. For all of the sub‐regions investigated, heavy precipitation contributed the most to changes in total precipitation amount. The results obtained from this study will be of value to those studying the response of northern Chinese ecosystems to climate change.

On the Current and Future Dry Spell Characteristics over Africa

Changes in precipitation frequency and intensity distribution over Africa will have a direct impact on dry spells and, therefore, will affect various climate sensitive sectors. In this study, the ability of the fifth generation of the Canadian Regional Climate Model (CRCM5) in simulating annual and seasonal dry spell characteristics is assessed for four precipitation thresholds (0.5 mm, 1 mm, 2 mm and 3 mm) over Africa. The dry spell characteristics considered are the number of dry days, number of dry spells and five-year return levels of maximum dry spell durations. The performance errors are assessed by comparing ERA-Interim driven CRCM5 with the Global Precipitation Climatology Project (GPCP) dataset, for the common 1997–2008 period. Lateral boundary forcing errors, i.e., errors in the CRCM5 simulation created by errors in the driving Canadian Earth System model (CanESM2) data—as well as the added value—of CRCM5 over CanESM2 are also assessed for the current climate. This is followed by an assessment of projected changes to dry spell characteristics for two future climates (2041–2070 and 2071–2100) simulated by both CRCM5 driven by CanESM2 and CanESM2 itself, for Representative Concentration Pathway (RCP) 4.5. Results suggest that CRCM5 driven by ERA-Interim has a tendency to overestimate the annual mean number of dry days and the five-year return level of the maximum dry spell duration in a majority of the regions while it slightly underestimates the number of dry spells. In general, the CRCM5 performance errors associated with the annual and seasonal dry spell characteristics are found to be larger in magnitude compared to the lateral boundary forcing errors. Projected changes to the dry spell characteristics for the 2041–2070 and 2071–2100 periods, with respect to the 1981–2010 period suggests significant changes in the tropics, with the mean number of dry days and the five-year return levels of maximum dry spell duration increasing, while the mean number of dry spell days decreases.

Changes in precipitation frequency and intensity in the vicinity of Taiwan: typhoon versus non-typhoon events

The hourly rainfall at 21 ground stations in Taiwan is used to investigate changes in the frequency, intensity, and duration of rainfall, which can be divided into typhoon and non-typhoon rainfall, in the period of 1970–2010. As a whole, the frequency of rainfall shows a decreasing trend for lighter rain and an increasing trend for heavier rain. Also, the typhoon rainfall shows a significant increase for all intensities, while the non-typhoon rainfall exhibits a general trend of decreasing, particularly for lighter rain. In rainfall intensity, both typhoon and non-typhoon rainfall extremes become more intense, with an increased rate much greater than the Clausius–Clapeyron thermal scaling. Moreover, rainfall extremes associated with typhoons have tended to affect Taiwan rainfall for longer in recent decades. The more frequent, intense and long-lasting typhoon rainfall is mainly induced by the slower translation speed of the typhoons over the neighborhood of Taiwan, which could be associated with a weakening of steering flow in the western North Pacific and the northern South China Sea.

Regional Perspective on Mechanisms for Tropical Precipitation Frequency and Intensity under Global Warming

Abstract From a global point of view, a shift toward more intense precipitation is often found in observations and global warming simulations. However, similar to changes in mean precipitation, these changes associated with precipitation characters, such as intensity and frequency, should vary with space. Based on the classification of the subregions for the tropics in Chou et al., changes in precipitation frequency and intensity and their association with changes in mean precipitation are analyzed on a regional basis in 10 coupled global climate models. Furthermore, mechanisms for these changes are also examined, via the thermodynamic and dynamic contributions. In general, the increase (decrease) of mean precipitation is mainly attributed to increases (decreases) in the frequency and intensity of almost all strengths of precipitation: that is, light to heavy precipitation. The thermodynamic contribution, which is associated with increased water vapor, is positive to both precipitation frequency and intensity, particularly for precipitation extremes, and varies little with space. On the other hand, the dynamic contribution, which is related to changes in the tropical circulation, is the main process for inducing the spatial variation of changes in precipitation frequency and intensity. Among mechanisms that induce the dynamic contribution, the rich-get-richer mechanism (the dynamic part), ocean feedback, and warm horizontal advection increase precipitation frequency and intensity, while the upped-ante mechanism, the deepening of convection, longwave radiation cooling, and cold horizontal advection tend to reduce precipitation frequency and intensity.

Precipitation manipulation experiments – challenges and recommendations for the future

Climatic changes, including altered precipitation regimes, will affect key ecosystem processes, such as plant productivity and biodiversity for many terrestrial ecosystems. Past and ongoing precipitation experiments have been conducted to quantify these potential changes. An analysis of these experiments indicates that they have provided important information on how water regulates ecosystem processes. However, they do not adequately represent global biomes nor forecasted precipitation scenarios and their potential contribution to advance our understanding of ecosystem responses to precipitation changes is therefore limited, as is their potential value for the development and testing of ecosystem models. This highlights the need for new precipitation experiments in biomes and ambient climatic conditions hitherto poorly studied applying relevant complex scenarios including changes in precipitation frequency and amplitude, seasonality, extremity and interactions with other global change drivers. A systematic and holistic approach to investigate how soil and plant community characteristics change with altered precipitation regimes and the consequent effects on ecosystem processes and functioning within these experiments will greatly increase their value to the climate change and ecosystem research communities. Experiments should specifically test how changes in precipitation leading to exceedance of biological thresholds affect ecosystem resilience and acclimation.

Mechanisms for Global Warming Impacts on Precipitation Frequency and Intensity

Global warming mechanisms that cause changes in frequency and intensity of precipitation in the tropics are examined in climate model simulations. Under global warming, tropical precipitation tends to be more frequent and intense for heavy precipitation but becomes less frequent and weaker for light precipitation. Changes in precipitation frequency and intensity are both controlled by thermodynamic and dynamic components. The thermodynamic component is induced by changes in atmospheric water vapor, while the dynamic component is associated with changes in vertical motion. A set of equations is derived to estimate both thermodynamic and dynamic contributions to changes in frequency and intensity of precipitation, especially for heavy precipitation. In the thermodynamic contribution, increased water vapor reduces the magnitude of the required vertical motion to generate the same strength of precipitation, so precipitation frequency increases. Increased water vapor also intensifies precipitation due to the enhancement of water vapor availability in the atmosphere. In the dynamic contribution, the more stable atmosphere tends to reduce the frequency and intensity of precipitation, except for the heaviest precipitation. The dynamic component strengthens the heaviest precipitation in most climate model simulations, possibly due to a positive convective feedback.