Total Amount Of Precipitation Research Articles

Arctic has been going through a transition from solid precipitation to liquid precipitation in spring

The changes of precipitation form have important impacts on mass balance and energy flux of the underlying Cryosphere that closely related to hydrological cycles and the health of the ecosystem over the Arctic. So far, most of land stations around Arctic record the total precipitation amount only, except for dozens of stations in Alaska and northern Canada, where the solid and liquid precipitation are recorded respectively. Based on these different precipitation form records and daily mean air temperature observations during 1961–2015, we developed a special standard of optimum temperature threshold to separate rainfall from the total precipitation. That is, if the air temperature is greater than the temperature threshold, the probability of precipitation occurring as rain is larger than 0.5, then we assume the precipitation falls in liquid form. We derived the seasonal optimum temperature threshold of 2.01°C (spring), 0.54°C (summer), 1.14°C (fall) and 1.17°C (mean annual), respectively. We did not discuss the situation in winter because of rare liquid precipitation observations. By using these temperature thresholds, we distinguished the solid and liquid phase from total precipitation archived at 253 stations over the northern Eurasia region and investigated their variation trend during 1961–2010. Results showed that the proportion of rainfall in total precipitation decreased with latitudes in the region north of 60°N. In general, we found the maximum and minimum of the rainfall to total precipitation ratio (RPR) in summer and winter. Further analysis demonstrated that the precipitation forms showed obvious seasonal and interannual variability. Specially, the spring RPR increased over most of the terrestrial Arctic (82.46% stations), 22.37% of which passed 95% statistical significance test, indicating that there was a general transition trend from solid precipitation to liquid precipitation in the spring Arctic continents over the past decades. In summer and autumn, there was obvious regional variability in the south of the research area, but in the arctic coastal stations the increasing trend appeared uniform. The RPR trends, respectively derived from the lower and upper limits of 95% confidence interval of temperature threshold, were highly consistent with the trend in the spatial distribution that derived from the optimum temperature threshold. Additionally, more precipitation had fallen as rainfall instead of snowfall in Alaska, Siberia and Northern Europe during the ablation season (March-July), which would make profound impacts on the Arctic land-atmosphere interaction.

Effect of drought on productivity in a Costa Rican tropical dry forest

Climate models predict that precipitation patterns in tropical dry forests (TDFs) will change, with an overall reduction in rainfall amount and intensification of dry intervals, leading to greater susceptibility to drought. In this paper, we explore the effect of drought on phenology and carbon dynamics of a secondary TDF located in the Santa Rosa National Park (SRNP), Costa Rica. Through the use of optical sensors and an eddy covariance flux tower, seasonal phenology and carbon fluxes were monitored over a four-year period (2013–2016). Over this time frame, annual precipitation varied considerably. Total precipitation amounts for the 2013–2016 seasons equaled 1591.8 mm (+14.4 mm SD), 1112.9 mm (+9.9 mm SD), 600.8 mm (+7.6 mm SD), and 1762.2 mm (+13.9 mm SD), respectively. The 2014 and 2015 (ENSO) seasonal precipitation amounts represent a 30% and 63% reduction in precipitation, respectively, and were designated as drought seasons. Phenology was affected by precipitation patterns and availability. The onset of green-up was closely associated with pre-seasonal rains. Drought events lead to seasonal NDVI minimums and changes in phenologic cycle length. Carbon fluxes, assimilation, and photosynthetic light use efficiency were negatively affected by drought. Seasonal minimums in photosynthetic rates and light use efficiency were observed during drought events, and gross primary productivity was reduced by 13% and 42% during drought seasons 2014 and 2015, respectively. However, all four growth seasons were net carbon sinks. Results from this study contribute towards a deeper understanding of the impact of drought on TDF phenology and carbon dynamics.

Variation of the Chemistry of the Dead Sea Brine as Consequence of the Decreasing Water Level

For many years, the Dead Sea suffers from an annual inflow deficiency of about one billion cubic meters, flood and baseflow. The water level changes are related to the majority of surface water inflows diverted for irrigation purposes, in addition to intensive loss of water by the high rate of evaporation and industrial water use. This causes the Dead Sea water level to decline about 35 m within the last 50 years for a long-term average of about 0.79 m per year. The changes in the hydrochemical composition were simulated experimentally to determine the changes that take place as a function of brine water evaporation level and its density. The Total Dissolved Solids (TDS) and the density of the Dead Sea water varies as a function of its water evaporation level changes. It was found that the density variation is not following a linear function with respect to water volume changes. But it follows the total amount of precipitate that occurred at different water levels. The electrical conductivity (EC) changes with respect to time and the prevailing temperature. There was no formula to calculate the high salinity of brine water above the normal ocean water. Consequently, the EC measurements were adopted to represent the Dead Sea water salinity. But in this research a converging factor (0.80971) has been found to convert the TDS values into salinity values. On contrary, the pH values revealed an inverse relationship with respect to the evaporation levels.

Model simulations with COSMO-SPECS: impact of heterogeneous freezing modes and ice nucleating particle types on ice formation and precipitation in a deep convective cloud

Abstract. In deep convective clouds, heavy rain is often formed involving the ice phase. Simulations were performed using the 3-D cloud resolving model COSMO-SPECS with detailed spectral microphysics including parameterizations of homogeneous and three heterogeneous freezing modes. The initial conditions were selected to result in a deep convective cloud reaching 14 km of altitude with strong updrafts up to 40 m s−1. At such altitudes with corresponding temperatures below −40 ∘C the major fraction of liquid drops freezes homogeneously. The goal of the present model simulations was to investigate how additional heterogeneous freezing will affect ice formation and precipitation although its contribution to total ice formation may be rather low. In such a situation small perturbations that do not show significant effects at first sight may trigger cloud microphysical responses. Effects of the following small perturbations were studied: (1) additional ice formation via immersion, contact, and deposition modes in comparison to solely homogeneous freezing, (2) contact and deposition freezing in comparison to immersion freezing, and (3) small fractions of biological ice nucleating particles (INPs) in comparison to higher fractions of mineral dust INP. The results indicate that the modification of precipitation proceeds via the formation of larger ice particles, which may be supported by direct freezing of larger drops, the growth of pristine ice particles by riming, and by nucleation of larger drops by collisions with pristine ice particles. In comparison to the reference case with homogeneous freezing only, such small perturbations due to additional heterogeneous freezing rather affect the total precipitation amount. It is more likely that the temporal development and the local distribution of precipitation are affected by such perturbations. This results in a gradual increase in precipitation at early cloud stages instead of a strong increase at later cloud stages coupled with approximately 50 % more precipitation in the cloud center. The modifications depend on the active freezing modes, the fractions of active INP, and the composition of the internal mixtures in the drops.

Spatial variability of concentration and aggressiveness of precipitation in North-East of Algeria

AbstractIn this study, the spatial variation of daily and monthly concentration precipitation index and its aggressiveness were used in 23 rainfall stations in the extreme north-east of Algeria over the period 1970–2010. The trend was analysed by the Mann–Kendall (MK) test. The results show that daily precipitation concentration index (CI) values are noticeably higher in places where the amount of total precipitation is low, the results of MK test show that areas of high precipitation concentration tend to increase. The seasonality and aggressiveness of precipitation are high in the eastern and western parts of the study region (eastern and central coastal of Constantine catchments), whereas a moderately seasonal distribution with low aggressiveness is found in the middle of the study area (plains and central Seybouse catchment). As a result, the modified Fournier index (MFI) has a significant correlation with annual precipitation, whereas theCIand monthly precipitation concentration index (PCI) show an opposite correlation in relation to annual precipitation.

Modelling the effect of changing precipitation inputs on deep soil water utilization

AbstractForests in the Southeastern United States are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change‐induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that access subsurface water resources. To address plant response to drought in both deep rooting and soil water utilization as well as soil drainage, we utilize a throughfall reduction experiment in a loblolly pine plantation of the Southeastern United States to calibrate and validate a hydrological model. The model was accurately calibrated against field measured soil moisture data under ambient rainfall and validated using 30% throughfall reduction data. Using this model, we then tested these scenarios: (a) evenly reduced precipitation; (b) less precipitation in summer, more in winter; (c) same total amount of precipitation with less frequent but heavier storms; and (d) shallower rooting depth under the above 3 scenarios. When less precipitation was received, drainage decreased proportionally much faster than evapotranspiration implying plants will acquire water first to the detriment of drainage. When precipitation was reduced by more than 30%, plants relied on stored soil water to satisfy evapotranspiration suggesting 30% may be a threshold that if sustained over the long term would deplete plant available soil water. Under the third scenario, evapotranspiration and drainage decreased, whereas surface run‐off increased. Changes in root biomass measured before and 4 years after the throughfall reduction experiment were not detected among treatments. Model simulations, however, indicated gains in evapotranspiration with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios but not when precipitation frequency was adjusted. Deep soil and deep rooting can provide an important buffer capacity when precipitation alone cannot satisfy the evapotranspirational demand of forests. How this buffering capacity will persist in the face of changing precipitation inputs, however, will depend less on seasonal redistribution than on the magnitude of reductions and changes in rainfall frequency.

Evaluating satellite-based precipitation products in monitoring drought events in southwest China

ABSTRACTSouthwest China (SWC) is one of the areas that has most frequently been affected by a variety of drought events in recent years. Satellite-based precipitation products with high spatial resolution, having greatly improved their accuracy and applicability, are expected to offer an alternative to improve drought monitoring. The purpose of this article is to evaluate the reliability of the Tropical Rainfall Measuring Mission (TRMM) V7 3B43 products using the observed monthly precipitation data obtained from 118 meteorological stations from 1998 to 2013 and to monitor the temporal and spatial variations of drought conditions using the Standardized Precipitation Index (SPI), which is derived by a non-parametric approach. The results showed that the TRMM 3B43 products performed well in terms of monthly precipitation, although they slightly overestimated the total precipitation amount, mainly in summer. They matched the observed data well, yielding high correlations and low biases in most parts of SWC. For drought assessment, the SPI based on monthly TRMM 3B43 data oscillated around zero and showed a consistent inter-annual variability compared with gauges. Moreover, the TRMM 3B43 showed similar temporal drought behaviour by capturing most of the drought events at various timescales, and both of them described similar spatial patterns of drought. The TRMM products precisely described the occurrence and development process of the 2009/2010 drought and revealed that compared to the 2009/2010 drought the 2011 drought was more severe and affected a larger area. In general, using the TRMM 3B43 product is suitable and credible for drought monitoring over SWC.

Dendroclimatic research on Scots pine growing under the conditions of the raised bog in the Volga-Kama region, Russia

The radial growth dynamics of Scots pine in a large raised bog located in the territory of the Volga-Kama Nature Reserve, Republic of Tatarstan, has been studied. The master chronology correlated positively with the total amount of precipitation in January and negatively with the mean monthly temperature in June. Based on a complex analysis of temperature and precipitation in different months using hierarchical regression trees, three scenarios resulting in increased, average, and decreased radial growth have been suggested.

Responses of normalized difference vegetation index (NDVI) to precipitation changes on the grassland of Tibetan Plateau from 2000 to 2015.

Precipitation change is an important factor in the inter-annual variation of grassland growth on the Tibetan Plateau. The total amount, distribution pattern and concentration time are three basic characteristics of precipitation change. The temporal and spatial characteristics of precipitation change were analyzed based on climate data of 145 meteorological stations on the Tibetan Plateau and nearby areas from 2000 to 2015. The total precipitation amount was characterized by annual precipitation, distribution pattern of precipitation during the year was characterized by improved precipitation concentration index (PCI), and precipitation centroid (PC) was defined to indicate the change in precipitation concentrated time. To better illustrate the response of grassland to precipitation change, vegetation growth status was characterized by the maximum value of normalized difference vegetation index (NDVImax). Results indicated that the annual precipitation and PCI had an apparent gradient across the whole plateau and the latest PC occurred in the southern plateau. NDVImax of alpine shrub grassland was significantly correlated with the change of PCI,increased with even distribution of precipitation during growth period, and limited by the total annual precipitation. Alpine meadow did not show significantly correlations with these three indices. The inter-annual variability of NDVImax of steppe was controlled by both PCI and PC. NDVImaxof alpine desert grassland was mainly controlled by annual precipitation. In addition to annual total amount of precipitation, the distribution characteristics of precipitation should be further considered when the influence of precipitation change on different types of vegetation on the Qinghai Tibet Plateau was studied.

Scale Effects of Water Saving on Irrigation Efficiency: Case Study of a Rice-Based Groundwater Irrigation System on the Sanjiang Plain, Northeast China

This research analyzed the scale effect of water saving in Bielahonghe (BLH) Basin, a rice-cultivating district on the Sanjiang Plain, Northeast China. Water budgets with different surface irrigation water supply ratios and water-saving measures were simulated with a semi-distributed water balance model. PFnws, representing the ratio of rice evapotranspiration to net water supply (the total amount of irrigation and precipitation minus the amount of water reused), was employed to assess the water use efficiency. Seven spatial scales (noted from S1 to S7), ranging from a single field (317.87 ha) to the whole basin (about 100,800 ha) were determined. PFnws values were quantified across scales and several water-saving measures, including water-saving irrigation regimes, canal lining, and a reduction of the surface water supply ratio (SWSR). The results indicated that PFnws increased with scale and could be calculated by a fitted power function (PFnws = 0.736Area0.033, R2 = 0.58). Furthermore, PFnws increased most prominently when the scale increased from S1 to S2. The water-saving irrigation regime (WSIR) had the most substantial water-saving effect (WSE) at S1. Specifically, PFnws improved by 21.2% at S1 when high-intensity WSIR was applied. Additionally, the WSE values of S3 and S5 were slightly higher than at other scales when the branch canal water delivery coefficient increased from 0.65 to 0.80 through canal lining. Furthermore, the PFnws at each scale varied with SWSR. Specifically, PFnws from S3 to S7 improved as SWSR decreased from 0.4 to 0.3 but remained approximately constant when SWSR decreased from 0.3 to 0.

Quantitative study on the blockage degree of pores due to asphaltene precipitation in low-permeability reservoirs with NMR technique

With the nuclear magnetic resonance (NMR) technology, a new experimental method was proposed to study the blockage degree of pores due to asphaltene precipitation during CO2 flooding in Low-Permeability Reservoirs. By comparing the T2 spectrum measured before and after CO2 flooding, the blockage degree by asphaltene precipitation was quantitatively determined for the pores with different sizes. It was found that, at the immiscible flooding stage, oil was mainly recovered from the larger pores (1.0–100.0 μm) and the asphaltene tended to precipitate in such pores. Compared with the larger pores, nearly no asphaltene precipitation was formed in the smaller pores (0.1–1.0 μm) at the immiscible stage. At CO2 injection pressures above the minimum miscibility pressure (MMP), asphaltene precipitation formed in the lager pores; precipitation also took place in the smaller pores, filling up a significant portion of space in the smaller pores. At the miscible flooding stage, the total amount of asphaltene precipitation was reduced. The observed permeability reductions correlate reasonably with the amount of asphaltene precipitation for all flooding stages. By analyzing the T2 spectrum in different pores before and after CO2 flooding, it was observed that the smaller pores were more apt to be blocked by the asphaltene precipitation than the larger pores. Since the asphaltene-blocking phenomena significantly affect the smaller pores, the core permeability may be substantially compromised after CO2 flooding.

Identifying the Monotonic Trend in Climate Change Parameter in Kluang and Senai, Johor, Malaysia

Presently, climate change plays an important role as it gives a serious impact to the living things on earth. Analyzing the trend of climate change is very important in identifying the pattern of changes because it can give an initial overview for future analysis. In this study, trend analysis was carried out to study the pattern of changes for five climate change parameters, such as total amount of monthly precipitation (mm), monthly average temperature (°C), monthly average global radiation (MJm–2), monthly average wind speed (m/s) and monthly average humidity (%) during the period of 1974 to 2010. Comparisons were made between two research stations, which were the Senai International Airport and Kluang Meteorological Stations. In this study, the Mann-Kendall trend test and Sen’s slope estimator test were used to identify the monotonic trend for these climate change parameters. As a result of this analysis, the precipitations showed no trend for both locations and the radiation showed no trend in Kluang from both analyses. Meanwhile, other parameters in Senai and Kluang showed a monotonic trend, according to the Tau value (Z) and the Sen’s slope value. The temperature shows a positive trend for both locations.

Calculation of precipitation during period of catastrophic flood 21-27 july 2008 in Ukrainian Carpathians

Intense precipitation event happened in Ukraine on 21-27 July 2008 leading to extreme flash floods in the Ukrainian Carpathians which are characterized by the return period of approximately 50 years. Besides favourable synoptic conditions leading to quasi-stationary low situated over Balkans and South-West part of Ukraine precipitation during this event was intensified by mountains. This lead to formation of the specific precipitation patterns in the Ukrainian Carpathians which was not adequately resolved by the existing measurement network.
 The purpose of this publication is application of the mesoscale meteorological model WRF with high resolution (1 km) for reconstruction of precipitation during flood in July, 2008 in the Ukrainian Carpathians and evaluation of the simulated results against measurements.
 Calculation of precipitation during the period of catastrophic summer flood in 2008 at the territory of Ukrainian Carpathians had been carried out with the use of meteorological model WRF. The precipitation field was well simulated for the period of maximum floods (July, 25-th) as compared to precipitation data measured at meteorological stations. However the second and lower peak of precipitation which happened during July, 27-th was underestimated by WRF. The reason of such underestimation is possibly the influence of boundary conditions on simulated results. The precipitation field formed during July, 25-th is elongated along the main ridge of the Ukrainian Carpathians and precipitation maximums on that date, reaching up to 70 mm/3 hours are situated above foothills of the Carpathians. On July, 27-th the precipitation maximums are shifted south-eastward, close to the boundary of the computational domain. The vertical crossections of the calculated meteorological fields demonstrate characteristic system of gravitational waves occurring in flow above mountains and sequence of convective cells situated mostly above the windward (north-eastern) hills and coinciding with the precipitation maximums. The depth of some of the convective cells reaches 10 km, which is supported by satellite data. The indirect evaluation of the calculated precipitation field is performed using the measured water discharge data at the watersheds of the rivers in Carpathians. For the period of maximum flood the relative precipitation amount at each watershed (over total precipitation amount at all water-sheds) appears to be approximately equal to relative water discharge of the corresponding watershed.
 In conclusion we could state that the precipitation field was well simulated by WRF for the period of maximum floods (25 July). High quality of simulated results is supported by comparison of the calculated and measured precipitation as well as with indirect juxtaposition of the calculated integral precipitation at the watersheds of Carpathian rivers and water discharges in the corresponding river outlets. The calculated results demonstratre that existing measurement network is too sparse to capture the details of the orographically enhanced precipitation field. The scarcity of the measurement network makes it difficult to evaluate integral and maximum characteristics of precipitation happening in the Ukrainian Carpathians.
 Directions for further research should include usage of the coupled mesoscale meteorological-distributed hydrological model chain for calculation and forecasting of meteorological and hydrological characteristics of floods.

Effects of biotic and abiotic factors on resistance versus resilience of Douglas fir to drought.

Significant increases in tree mortality due to drought-induced physiological stress have been documented worldwide. This trend is likely to continue with increased frequency and severity of extreme drought events in the future. Therefore, understanding the factors that influence variability in drought responses among trees will be critical to predicting ecosystem responses to climate change and developing effective management actions. In this study, we used hierarchical mixed-effects models to analyze drought responses of Pseudotsuga menziesii in 20 unmanaged forests stands across a broad range of environmental conditions in northeastern Washington, USA. We aimed to 1) identify the biotic and abiotic attributes most closely associated with the responses of individual trees to drought and 2) quantify the variability in drought responses at different spatial scales. We found that growth rates and competition for resources significantly affected resistance to a severe drought event in 2001: slow-growing trees and trees growing in subordinate canopy positions and/or with more neighbors suffered greater declines in radial growth during the drought event. In contrast, the ability of a tree to return to normal growth when climatic conditions improved (resilience) was unaffected by competition or relative growth rates. Drought responses were significantly influenced by tree age: older trees were more resistant but less resilient than younger trees. Finally, we found differences between resistance and resilience in spatial scale: a significant proportion (approximately 50%) of the variability in drought resistance across the study area was at broad spatial scales (i.e. among different forest types), most likely due to differences in the total amount of precipitation received at different elevations; in contrast, variation in resilience was overwhelmingly (82%) at the level of individual trees within stands and there was no difference in drought resilience among forest types. Our results suggest that for Pseudotsuga menziesii resistance and resilience to drought are driven by different factors and vary at different spatial scales.

Distributions of Tropical Precipitation Cluster Power and Their Changes under Global Warming. Part I: Observational Baseline and Comparison to a High-Resolution Atmospheric Model

Abstract The total amount of precipitation integrated across a precipitation feature (contiguous precipitating grid cells exceeding a minimum rain rate) is a useful measure of the aggregate size of the disturbance, expressed as the rate of water mass lost or latent heat released (i.e., the power of the disturbance). The probability distribution of cluster power is examined over the tropics using Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite-retrieved rain rates and global climate model output. Observed distributions are scale-free from the smallest clusters up to a cutoff scale at high cluster power, after which the probability drops rapidly. After establishing an observational baseline, precipitation from the High Resolution Atmospheric Model (HiRAM) at two horizontal grid spacings (roughly 0.5° and 0.25°) is compared. When low rain rates are excluded by choosing a minimum rain-rate threshold in defining clusters, the model accurately reproduces observed cluster power statistics at both resolutions. Middle and end-of-century cluster power distributions are investigated in HiRAM in simulations with prescribed sea surface temperatures and greenhouse gas concentrations from a “business as usual” global warming scenario. The probability of high cluster power events increases strongly by end of century, exceeding a factor of 10 for the highest power events for which statistics can be computed. Clausius–Clapeyron scaling accounts for only a fraction of the increased probability of high cluster power events.

Spatial and temporal patterns of dry spells in western Turkey

An analysis of spatial and temporal variations of dry spells was carried out for western Turkey using daily precipitation data of 28 stations from 1966 to 2011. Three indices and four levels of precipitation-per-day threshold were considered. Indices are number (NDS), mean length (MDS) and maximum length (MxDS) of dry spells, and the thresholds are 0.1, 1, 5 and 10 mm/day. The results showed that a general decreasing gradient from north-east to south-west is evident for NDS with exceptionally higher values at south-west at 10 mm/day threshold. Mean MDS depicts an opposite pattern to that of NDS particularly for 0.1 and 1 mm/day. Longer mean MDS values are observed at western and eastern parts for 5 and 10 mm/day. For all threshold levels, there is a clear increasing gradient from north-east to south-west for mean MxDS. Trend analysis showed that the majority of trends of the indices at all thresholds are statistically non-significant at 95% level. It can be concluded that the study area as a whole has experienced a general and slight (statistically non-significant) decreasing tendency for NDS but a general and slight (statistically non-significant) increasing tendency for MDS and MxDS. Over the same period, total annual precipitation has shown statistically non-significant decline at almost all stations. It can be concluded that the slightly decreasing tendency in total annual precipitation has been accompanied by slightly decreasing NDS and by slightly increasing MDS and MxDS. This suggests that the study area has received less precipitation and experienced less frequent but longer duration of dry spells over the period 1966–2011. The droughts in the study area have become relatively worse in terms of not only the total amount of precipitation but also duration of dry periods, although dry periods have occurred less frequently.

The response of a simulated mesoscale convective system to increased aerosol pollution: Part I: Precipitation intensity, distribution, and efficiency

Mesoscale Convective Systems (MCSs) are important contributors to rainfall in the High Plains of the United States and elsewhere in the world. It is therefore of interest to understand how different aerosols serving as cloud condensation nuclei (CCN) may impact the total amount, rates and spatial distribution of precipitation produced by MCSs. In this study, different aerosol concentrations and their effects on precipitation produced by an MCS are examined by simulating the 8 May 2009 “Super-Derecho” MCS using the Regional Atmospheric Modeling System (RAMS), a cloud-resolving model (CRM) with sophisticated aerosol and microphysical parameterizations. Three simulations were conducted that differed only in the initial concentration, spatial distribution, and chemical composition of aerosols. Aerosol fields were derived from the output of GEOS-Chem, a 3D chemical transport numerical model. Results from the RAMS simulations show that the total domain precipitation was not significantly affected by variations in aerosol concentrations, however, the pollution aerosols altered the precipitation characteristics. The more polluted simulations exhibited higher precipitation rates, higher bulk precipitation efficiency, a larger area with heavier precipitation, and a smaller area with lighter precipitation. These differences arose as a result of aerosols enhancing precipitation in the convective region of the MCS while suppressing precipitation from the MCS's stratiform-anvil. In the convective region, several processes likely contributed to an increase of precipitation. First, owing to the very humid environment of this storm, the enhanced amount of cloud water available to be collected overwhelmed the reduction in precipitation efficiency associated with the aerosol-induced production of smaller droplets which led to a net increase in the conversion of cloud droplets to precipitation. Second, higher aerosol concentrations led to invigoration of convective updrafts which enhanced precipitation in accordance to the convective invigoration hypothesis. The reduction in stratiform precipitation in the more polluted simulations was found to be attributed to the presence of greater aerosol number concentrations that reduced both collision-coalescence and riming. Analysis of back trajeocty flow showed that the air feeding the stratiform-anvil originated within the free troposphere, by mesoscale ascent. Therefore, increased aerosol pollution at higher elevations impacted the stratiform precipitation formation within the simulated MCS. As a consequence, the more polluted simulations produced the smallest precipitation from the MCS stratiform-anvil region. In Part II the impact of aerosols on the severe winds produced by this storm is examined.

Temporal change of spatial heterogeneity and its effect on regional trend of annual precipitation heterogeneity indices

AbstractA statistical test on climate and hydrological series from different spatial resolution could obtain different regional trend due to spatial heterogeneity and its temporal variability. In this study, annual series of the precipitation heterogeneity indices of concentration index (CI) and the number of wet days (NW) along with annual total amount of precipitation were calculated based on at‐site daily precipitation series during 1962–2011 in the headwater basin of the Huaihe River, China. The regional trends of the indices were first detected based on at‐site series by using the aligned and intrablock methods, and field significance tests that consider spatial heterogeneity over sites. The detected trends were then compared with the trends of the regional index series derived from daily areal average precipitation (DAAP), which averages at‐site differences and thus neglects spatial heterogeneity. It was found that the at‐site‐based regional test shows increasing trends of CI and NW in the basin, which follows the test on individual sites that most of sites were characterized by increasing CI and NW. However, the DAAP‐derived regional series of CI and NW were tested to show a decreasing trend. The disparity of the regional trend test on at‐site‐based regional series and the DAAP‐derived regional series arises from a temporal change of the spatial heterogeneity, which was quantified by the generalized additive models for location, scale, and shape. This study highlights that compared with averaging indices, averaging at‐site daily precipitation could lead to an error in the regional trend inference on annual precipitation heterogeneity indices. More attention should be paid to temporal variability in spatial heterogeneity when data at large scales are used for regional trend detection on hydro‐meteorological events associated with intra‐annual heterogeneity.

Assessment of deterministic PMF modelling approaches

ABSTRACTProbable maximum flood (PMF) event estimation has challenged the scientific community for many years. Although the concept of the PMF is often applied, there is no consensus on the methods that should be applied to estimate it. In PMF estimation, the spatio-temporal representation of the probable maximum precipitation (PMP) as well as the choice of modelling approach is often not theoretically founded. Moreover, it is not clear how these choices influence PMF estimation itself. In this study, combinations of three different spatio-temporal PMP representations and three different modelling approaches are applied to determine the PMF of a mesoscale basin keeping the antecedent catchment conditions and the total precipitation amount constant. The nine resulting PMF estimations are used to evaluate each combination of methods. The results show that basic methods allow for a rough estimation of the PMF. In cases where a physically plausible and reliable estimation is required, sophisticated PMP and PMF estimation approaches are recommended.EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR A. Viglione

Quantifying agricultural drought in tallgrass prairie region in the U.S. Southern Great Plains through analysis of a water-related vegetation index from MODIS images

Severe droughts in the Southern Great Plains (SGP: Kansas, Oklahoma, and Texas) in recent years have reduced the productivity of tallgrass prairie and resulted in substantial economic losses to the beef cattle industry in this region. Understanding spatial and temporal patterns of agricultural drought in the SGP can help ranchers to develop and implement drought mitigation strategies. In this study, the Land Surface Water Index (LSWI), calculated from the Moderate Resolution Imaging Spectroradiometer (MODIS) near infrared and shortwave infrared bands, was used to assess agricultural drought in the tallgrass prairie region of the SGP during 2000–2013. The number of consecutive days with LSWI <0 (DNLSWI) during the growing season was defined as the drought duration, which, was then used to identify and analyze frequency of summer drought and whole growing season drought (WGSD). The spatial pattern of DNLSWI was consistent with the east-to-west decreasing precipitation gradient across the SGP region. Summer drought duration as depicted by the DNLSWI in the western portion of the study area was around one and a half month. The occurrence of WGSD increased from one year in the east to up to six years in the west, demonstrating the susceptibility of the tallgrass prairie region to drought. In addition to the total amount of precipitation, its intra-annual distribution also played an important role in drought development. A comparison with other widely used national drought products, namely the Evaporative Stress Index (ESI), the Vegetation Drought Response Index (VegDRI), and the United States Drought Monitor (USDM), shows that LSWI-based drought has good agreement with ESI and USDM. Quantitative analyses indicate that LSWI-based drought agreed better with ESI in severe drought conditions than in moderate or pre-drought conditions. Severe drought periods characterized by the USDM also had low LSWI values. The areas affected by drought derived from the LSWI-based drought index were significantly correlated with hay production. As an indicator of vegetation water stress at moderate spatial resolution (∼500m), the LSWI has the potential to show drought conditions for an individual ranch and offer guidance for drought mitigation activities and livestock production.