Long-term Annual Precipitation Research Articles

Comparison of water regimes of two dump catchments in the Krušné hory Mts. (Czech Republic) in dry years using a hydrological balance

The dump catchments water regime optimization is one of fundamental recultivation operations in areas devastated after surface coal mining. Two dump catchments (at Radovesice and Loket in the Krušné hory Mts., Czech Republic) were selected to study whether their hydrological balance allows to keep life in them on a sufficiently natural level. The WBCM-6 water balance model was implemented. Different hydrological conditions of the mentioned dump catchments located ca. 90 km apart were compared. The Radovesice catchment lies in a precipitation shadow and suffers from a much greater precipitation deficiency than the Loket one. Its long-term annual precipitation deficit makes about 100 mm. Based on the analysis of the dry year 2003 growing season, biotechnical hydrological measures, in particular cascades of small reservoirs, were proposed.

Uncertainties in the Estimation of Global Observational Network Datasets of Precipitation over West Africa

This study assessed the uncertainty in estimating long-term (1971-2010) mean precipitation, its inter-annual variability, and linear trend of three network observation datasets over West Africa. A reference data, defined as a multi-dataset ensemble of precipitation observations of the Climate Research Unit (CRU) of the University of East Anglia, the Global Precipitation Climatology Centre (GPCC) and the University of Delaware (UDEL), all at horizontal resolutions of 0.5° by 0.5° were obtained and used in this study. Uncertainties in these climatological parameters of precipitation at both annual and seasonal time scales were examined in terms of inter-dataset variability using signalto- noise ratio (SNR), correlation, root-mean-square errors and the normalised standard deviation. Results showed that the mean, inter-annual variability and trends climatology varied for different datasets. The three datasets had good agreement (SNR>5) in terms of the annual mean precipitation and its inter-annual variability in most parts of West Africa. However, the agreement between the datasets was poor in the very dry Sahel parts of northern Niger, Mali, and Mauritania (SNR ≤ 1) due to very little precipitation and possibility of relatively low station density in these regions of complex terrain. In terms of correlation (0.89 ≤ r ≤ 0.98), and normalised standard deviation, NSD (0.8 ≤ NSD ≤ 1.7), the uncertainties in the spatial variations in linear trend were larger than mean precipitation and their inter-annual variability for both annual and seasonal scales. The long-term annual precipitation trend in the region is highly uncertain except in a few small areas.

Investigation of hydrological drought using Cumulative Standardized Precipitation Index (SPI 30) in the eastern Mediterranean region (Damascus, Syria)

The Eastern Mediterranean region has been exposed to drought episodes, which have been occurring more frequently during the last decades. The objective of the present paper is to study the precipitation regime of the Damascus (Mazzeh) meteoric station by analysing drought characteristics using the Standardized Precipitation Index (SPI) and comparing this with the drought in Cyprus. The cumulative drought conceptis proposed to characterize long-term hydrologic drought, which affects the shallow groundwater productivity in terms of quantity and quality. Gamma probability distribution was fitted to the long-term annual precipitation in Damascus from 1918–1919 to 2007–2008 (n = 90 years). Generally, a decreasing trend of 17% to the mean annual rainfall of Damascus and 13% to the mean annual rainfall of Cyprus was estimated between 1970 and 2000. The SPI identifies three major extended drought periods: (1) 9 years of severe drought (1954–1963) with an average 20% precipitation deficit per year compared to the mean. (2) 8 years of severe drought (1983–1991) with a 27% deficit per year on average. (3) 9 years of extreme drought (1993–2002) with a 31% deficit per year on average. The cumulative standardized precipitation index (SPI 30) demonstrates positive values for the first period and is indicative of having no effect on the global water balance. SPI 30 exhibits sensitive equilibrium with near zero values / a near zero value (±1.5) for the second period. For the third period, however, the SPI 30 decreases below −10 indicating an extreme hydrological drought that has negative consequences on the recent groundwater recharge. It is required to develop and implement a sustainable groundwater management strategy to reduce long-terms drought risks. Generally, the SPI 30 in Cyprus is parallel to that in Damascus with a 3–5 year delay. Thus, the central zone of the Eastern Mediterranean region is facing big challenges and has been suffering from three decades of moderate to severe hydrological drought (SPI 30=−5 to −10) causing a severe decrease in springs discharges of the region. Therefore, in order to reduce the climate change effects on water resources, it is necessary to adopt a sustainable proactive management plan during the frequent severe droughts.

Thirty Year Analysis of Forest and Scrub Canopy Cover on the Big Sur Coast of California using Landsat Imagery

The potential for negative effects such as habitat loss and high severity wildfires on endemic and threatened biological resources on the United States Pacific coast from recent climate warming has received increasing attention. This study was designed to quantify, for the first time, variations in forest and coastal bluff scrub canopy density and related growth rates using 30 consecutive years of April-to-June Landsat satellite image data for the central California coast around Big Sur. A trend model was fit to multi-year Landsat NDVI time series using least squares non-linear regression on time. Analysis showed that annual growth rates for coast redwood stands in the Big Sur area, the southern-most range for Sequoia sempervirens on the Pacific coast, have been depressed by periods of drought that exceeded -1.2 standard deviations of long-term annual precipitation. There was no evidence from the Landsat record that recent large wildfires have affected region-wide coast redwood stand structure or growth rates. Nonetheless, extensive wildfires of 2008 did have a marked (albeit temporary) impact on canopy density of the region’s mixed hardwood and Coulter pine forest zones, equivalent to the extreme drought effects of 1990-1991 and 2013-2014 on these higher elevation forest zones.

A 22 month record of surface meteorology and energy balance from the ablation zone of Brewster Glacier, New Zealand

AbstractMulti-annual records of glacier surface meteorology and energy balance are necessary to resolve glacier–climate interactions but remain sparse, especially in the Southern Hemisphere. To address this, we present a record from the ablation zone of Brewster Glacier, New Zealand, between October 2010 and September 2012. The mean air temperature was 1.2°C at 1760 m a.s.l., with only a moderate temperature difference between the warmest and coldest months (∼8°C). Long-term annual precipitation was estimated to exceed 6000 mm a−1, with the majority of precipitation falling within a few degrees of the freezing level. The main melt season was between November and March (83% of annual ablation), but melt events occurred during all months. Annually, net radiation was positive (a source of energy) and supplied 64% of the melt energy, driven primarily by net shortwave radiation. Net longwave radiation was often positive during cloudy conditions in summer, demonstrating the radiative importance of clouds during melt. Turbulent sensible and latent heat fluxes were directed towards the surface in the summer months, accounting for just over a third of the energy for melt (34%). The energy gain associated with rainfall was small except during heavy events in summer.

Seasonal patterns of Mediterranean evergreen woodlands (Montado) are explained by long-term precipitation

In temperate areas, vegetation seasonality and phenology have been mostly associated with temperature changes both in space and time. In drylands, where water is the most limiting factor, we expect that they strongly respond to water availability. The degree to what that response depends more on precipitation that occurred when vegetation seasonality and phenology were measured, or on the long-term precipitation, is not fully known. We hypothesize that in drylands, long-term precipitation better explains the patterns of seasonality and phenology metrics than concurrent one, due to constrains imposed by ecosystem legacy. We correlated long-term precipitation (30 years normal) and concurrent precipitation (12 years) to several seasonal metrics (MODIS, average of 12 years) measured in a savannah-like system, Mediterranean evergreen woodlands, located in southwest Europe (Portugal). We observed that seasonal metrics of productivity and phenology were more significantly related with long-term precipitation than with concurrent precipitation. Comparing the extremes of our gradient we found that drier areas (c. 496mm long-term annual precipitation) showed average growth cycles of annual plants 25 days shorter and ended 16 days sooner than more rainy regions (c. 739mm). Evergreen vegetation productivity was shown to be c. 30% lower in drier areas. Moreover, productivity and phenology metrics were non-linearly related to the long-term precipitation, suggesting both are particularly constrained below 600–650mm. These results suggest a memory effect in the response of vegetation to climate, most probably associated to legacies on soil characteristics and on plant community. It also indicates the existence of ecosystem response thresholds in vegetation's response to precipitation along ecosystem transitions. Overall, this method can be used to track ecosystem services over space in drylands and for managing ecosystems for both mitigation and adaptation to climate change.

A 250-year annual precipitation reconstruction and drought assessment for Cyprus from Pinus brutia Ten. tree-rings

Precipitation around Cyprus, a relatively small island, is generally consistent in year-to-year variation in all dimensions except amplitude, with the higher elevations in the west generally receiving more precipitation. An annual record of precipitation was found in tree-rings of the predominant pine species, Pinus brutia Ten., which grows from the lower foothills up to 1400 m in altitude across the island. Tree-ring chronologies from four sites in west-central Cyprus are used here to reconstruct the annual September to August precipitation and a drought record for AD 1830-2006, with the drought reconstruction extending back to 1756. A minimum of 40% of the variance in annual precipitation and drought occurrence is explained by the variance in the tree-ring widths in all cases. Our drought assessment indicates that, on average, annual droughts occur once every 5 years and sustained droughts, 2-6 years in length, have occurred in small clusters of time, from 1806-1824, 1915-1934 and 1986-2000, when the winter North Atlantic Oscillation was in a predominantly positive phase. These results suggest that a sustained drought period has a mean return time probability of one in 70-100 years. This study provides the first long-term annual precipitation reconstruction and drought assessment at low to mid-elevations for Cyprus and will aid in future plans for drought mitigation.

Long-term behaviour of 137Cs in spruce bark in coniferous forests in the Czech Republic

Activity concentrations of 137Cs were detected in more than 400 outer spruce bark samples collected at sites variably affected by Chernobyl fallout across the Czech Republic in 1995 and 2010. The temporal changes in the 137Cs activities were found. The mean effective half-life (TEF) for 137Cs in spruce bark was 9.6 years, and the mean environmental half-life (TE) was 14 years. The effective half-lives were significantly higher in areas with higher long-term annual precipitation sums. Coefficient a in linear regression y = ax + b of half-lives on precipitation sums was 0.015 y mm−1 for TEF and 0.036 y mm−1 for TE. The aggregated transfer factor of 137Cs from soil to bark was determined and the pre-Chernobyl bark contamination related to year 2010 was estimated.

Spatio-temporal variation of precipitation in the Three-River Headwater Region from 1961 to 2010

Based on a monthly dataset of precipitation time series (1961–2010) from 12 meteorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province, China, the spatio-temporal variation and abrupt change analysis of precipitation were examined by using moving average, linear regression, spline interpolation, the Mann-Kendall test and so on. Major conclusions were as follows. (1) The long-term annual and seasonal precipitation in the study area indicated an increasing trend with some oscillations during 1961–2010; however, the summer precipitation in the Lantsang (Lancang) River Headwater Region (LARHR), and the autumn precipitation in the Yangtze River Headwater Region (YERHR) of the THRHR decreased in the same period. (2) The amount of annual precipitation in the THRHR and its three sub-headwater regions was greater in the 1980s and 2000s. The springs were fairly wet after the 1970s, while the summers were relatively wet in the 1960s, 1980s and 2000s. In addition, the amount of precipitation in the autumn was greater in the 1970s and 1980s, but it was relatively less for the winter precipitation, except in the 1990s. (3) The normal values of spring, summer, winter and annual precipitation in the THRHR and its three sub-headwater regions all increased, but the normal value of summer precipitation in the LARHR had a negative trend and the normal value of winter precipitation declined in general. (4) The spring and winter precipitation increased in most of the THRHR. The summer, autumn and annual precipitation increased mainly in the marginal area of the west and north and decreased in the regions of Yushu, Zaduo, Jiuzhi and Banma. (5) The spring and winter precipitation in the THRHR and its three sub-headwater regions showed an abrupt change, except for the spring precipitation in the YARHR. The abrupt changes of spring precipitation were mainly in the late 1980s and early 1990s, while the abrupt changes of winter precipitation were primary in the mid-to late 1970s. This research would be helpful for further understanding the trends and periodicity of precipitation and for watershed-based water resource management in the THRHR.

Changes in rainfall patterns in the eastern area of La Pampa province, Argentina

The eastern area of the Province of La Pampa, Argentina lies in a transition zone between the humid temperate climate stretching east and the steppe climate stretching west. The area is very sensitive to changes in precipitation patterns, especially when changes are sudden and there is no time to take adaptive measures to cope with the impacts of climate change. In such cases, agricultural production and the balance of the environment are threatened by potential disaster. In order to determine the long-term occurrence of such phenomena, long-term annual precipitation series (1921–2009) from 14 stations in the study area were analyzed using the procedure of hydrometeorological series segmentation. The results for the study period show a succession of abrupt increases, with annual precipitation increasing by about 30%. Each increase in rainfall can be seen as a fostering factor for the expansion of crop planted area in the following years. However, in recent years, there has been an abrupt and significant decrease in precipitation with a marked return to the conditions that prevailed at the beginning of the period. Because agriculture intensified during the period of increased rainfall, the carrying capacity of the environment could be exceeded if rainfall continues to decrease over a long period of time, causing a decline in production accompanied by environmental degradation.

Homogeneity and Trend Analysis of Hydrometeorological Data of the Eastern Black Sea Region, Turkey

Eastern Black Sea Region in northeastern part of Turkey has the highest precipitation total in the country, approaching 2500 mm per a year. It is therefore an important region as it frequently encounters with flash floods due to heavy rains. For future planning of water resources, environment and urbanization, it is important to know the expected behavior of hydrometeorological processes, mainly precipitation and flow. Due to these facts, in this study, homogeneity of long-term annual precipitation and streamflow series of the Eastern Black Sea Region, Turkey is checked using double mass curve method and trends are determined by means of the Mann-Kendall test. The data network consists of 38 precipitation gauging stations and 40 flow gauging stations across the Eastern Black Sea Region. It is found that 27 precipitation stations out of 38 are homogeneous and no trend is available. Out of the remaining stations, nine are found non-homogeneous and four with trend. For annual flow data, it is found that 22 stations out of 40 are homogeneous and no trend is available. The remaining 18 stations are found non-homogeneous, among which 5 stations have trend at the same time.

Spatio‐temporal precipitation change assessments over Turkey

AbstractThe availability of water, and its quality, are among the chief growing concerns that are expected to cause serious questions over the sustainability of the Mediterranean region especially under the present climate change impacts, in general, and over the water resources of Turkey, in particular, due to precipitation pattern variability and sensitivity at arid and semi‐arid regions within the country. In order to assess climate impacts concerning precipitation over Turkey, expected spatio‐temporal changes are examined by considering precipitation time series at 165 stations across the country covering the period from 1961 to 2008 for almost 5 decades. Methodologically, homogeneity and Mann‐Kendall rank correlation trend tests are applied at each station for the identification of statistically significant trends. Long‐term annual precipitation averages indicate a decreasing trend with some oscillations during the last 5 decades. However, in more refined periods, average precipitation decreased during 1968–1973 and 1998–2008, whereas it increased during 1973–1981 and 1989–1998. As a result, there is a significant decrease of about 12, 13, and 35% at all stations in annual, rainy period, and winter season total precipitations, respectively. On the other hand, increases occurred at 4, 3 and 19% of all stations in annual, rainy, and autumn season, respectively. Copyright © 2011 Royal Meteorological Society

Generalized Mediterranean Annual Water Yield Model: Grunsky’s Equation and Long-Term Average Temperature

To estimate mean annual water yield on ungauged watersheds, regional regression equations have been developed that are a function of upstream area, precipitation, and temperature, and are commonly used. In this study, the 100-year old Grunsky equation is used as the foundation for a fully implemented generalized Mediterranean water yield model that is based on long-term annual precipitation and temperature. The work here (1) extends and generalizes Grunsky’s equation beyond its original conditions, (2) establishes an underlying hydro-climate generalized model for average annual Mediterranean watershed water yield and loss calculation, and (3) applies the validated model to estimate watershed water yield and predict potential water yield response to watershed temperature and precipitation. The water yield model was applied to watersheds in coastal California, southern France, and Portugal, but might be applied to other Mediterranean sites for which precipitation and temperature data are available. It also ...

How are seasonal prediction skills related to models’ performance on mean state and annual cycle?

Given observed initial conditions, how well do coupled atmosphere–ocean models predict precipitation climatology with 1-month lead forecast? And how do the models’ biases in climatology in turn affect prediction of seasonal anomalies? We address these questions based on analysis of 1-month lead retrospective predictions for 21 years of 1981–2001 made by 13 state-of-the-art coupled climate models and their multi-model ensemble (MME). The evaluation of the precipitation climatology is based on a newly designed metrics that consists of the annual mean, the solstitial mode and equinoctial asymmetric mode of the annual cycle, and the rainy season characteristics. We find that the 1-month lead seasonal prediction made by the 13-model ensemble has skills that are much higher than those in individual model ensemble predictions and approached to those in the ERA-40 and NCEP-2 reanalysis in terms of both the precipitation climatology and seasonal anomalies. We also demonstrate that the skill for individual coupled models in predicting seasonal precipitation anomalies is positively correlated with its performances on prediction of the annual mean and annual cycle of precipitation. In addition, the seasonal prediction skill for the tropical SST anomalies, which are the major predictability source of monsoon precipitation in the current coupled models, is closely link to the models’ ability in simulating the SST mean state. Correction of the inherent bias in the mean state is critical for improving the long-lead seasonal prediction. Most individual coupled models reproduce realistically the long-term annual mean precipitation and the first annual cycle (solstitial mode), but they have difficulty in capturing the second annual (equinoctial asymmetric) mode faithfully, especially over the Indian Ocean (IO) and Western North Pacific (WNP) where the seasonal cycle in SST has significant biases. The coupled models replicate the monsoon rain domains very well except in the East Asian subtropical monsoon and the tropical WNP summer monsoon regions. The models also capture the gross features of the seasonal march of the rainy season including onset and withdraw of the Asian–Australian monsoon system over four major sub-domains, but striking deficiencies in the coupled model predictions are observed over the South China Sea and WNP region, where considerable biases exist in both the amplitude and phase of the annual cycle and the summer precipitation amount and its interannual variability are underestimated.

Abrupt changes in rainfall in the Eastern area of La Pampa Province, Argentina

The eastern area of La Pampa Province, Argentina, lies in a transition zone between the humid temperate climate stretching east and the steppe climate stretching west. The area is thus very sensitive to abrupt changes in rainfall. In order to determine the long-term occurrence of such phenomena, long-term annual precipitation series (1921–2004) from 17 stations in the study area were analyzed using the Buishand and Pettitt tests. Results showed a sharp increase in annual rainfall at the southern stations in the 1960s and at the northern and central stations in the 1970s. Increased rainfall can be considered one of the reasons for the subsequent expansion in land planted to crops in the region. While a rapid increase in rainfall can be seen as positive, some researchers believe that if an abrupt decrease in rainfall occurred in future and continued for long, the carrying capacity of the environment could be exceeded, leading to decreased production and environmental degradation.

An ecohydrological modelling approach for assessing long-term recharge rates in semiarid karstic landscapes

An ecohydrological water balance method based on the hydrological equilibrium hypothesis was developed to estimate long-term annual recharge rates in semiarid karstic landscapes. Recharge was predicted from the difference between long-term annual precipitation and evapotranspiration rates. A multiple regression interpolation approach was used to compute precipitation. Evapotranspiration was quantified from the deviations between the observed local value of the normalised difference vegetation index (NDVI) and, the predicted minimum and maximum NDVI values for two hydrologically-well defined reference conditions representing the minimum and maximum vegetation density given a local long-term water availability index. NDVI values for the reference conditions (NDVImin and NDVImax) were estimated from an empirically-based boundary analysis. Evapotranspiration rates for the reference conditions were estimated using a monthly water budget model that integrates the roles of the soil water holding capacity and a climate-driven evaporative coefficient (k) representing the mean annual conductance of the vegetation canopy. The methodology was tested in Sierra de Gador (SE Spain), where predicted evapotranspiration and recharge rates compared well with local and regional scale estimates obtained from independent methods. A sensitivity analysis showed that NDVImax and k are the parameters that mostly affect our model’s evapotranspiration and recharge estimates.

SOIL ORGANIC CARBON SEQUESTRATION RATES IN TWO LONG-TERM NO-TILL EXPERIMENTS IN OHIO

The effectiveness of no-till (NT) farming in reducing loss of soil organic matter (SOM) depends on climate and soil properties. Soil samples were obtained from two long-term experiments that were designed to study the impact of tillage systems on crop yields. However, the objectives of this experiment were to assess the impact of NT on soil organic carbon (SOC) sequestration rate and other soil properties and to estimate historic depletion of SOC under different soil management practices with reference to the undisturbed wooded control. The two long-term experiments in Ohio studied were those sited at South Charleston and Hoytville. The South Charleston (83° 30′ W and 39° 48′ N) experiment was established in 1962 on Crosby silt loam (fine mixed, mesic Aeric Ochraqualf). The site has long-term annual temperature and precipitation of 10.8 °C and 1043 mm, respectively. Tillage treatments for continuous corn (Zea mays) were NT, chisel plow (CP), and moldboard plow (MP). The Hoytville (84° 04′ W and 41° 03′ N) experiment was established in 1987 on Hoytville clay loam (fine, illitic mesic Mollic Epiaqualfs) soil. The site has long-term annual temperature and precipitation of 9.9 °C and 845 mm, respectively. There were two crop rotations: (i) 2-year corn-soybean (Glycine max) rotation with NT and subsoiling and (ii) 3-year corn-soybean-oat (Avena sativa) rotation with NT, CP, and rotational tillage soil management. The Hoytville clay site is poorly drained, has higher clay content, and higher and more even by distributed antecedent level of SOC in the soil profile than does the South Charleston silt loam soil. No-till increased SOC and N pools in the 0 to 5-cm layer in silt loam soil but had no effect in clay soil. The rate of SOC sequestration in the silt-loam soil under NT was 175 kg C ha−1 y−1. The silt loam soil had higher SOC and N stratification ratios in NT than in MP and CP treatments, whereas the stratification ratios were low and similar in all treatments in the clayey soil. For both soils, there were no differences between tillage treatments in several soil properties including texture, available water capacity, hydraulic conductivity (Ks), and cation exchange capacity. The NT decreased soil bulk density and pH in the 0 to 15-cm layer in the silt loam soil. The plow till treatments had a small impact on soil aggregation in clayey soil. The decline in water-stable aggregates with reference to NT was no more than one sixth. In the silt loam soil, however, the water-stable aggregates in plow till treatments were merely one third of that in the NT treatment. The historic loss of the SOC pool for 0 to 30-cm depth under agricultural land use was 25 to 35% in silt loam and 19 to 25% in the clayey soil.

Utility of Penman–Monteith, Priestley–Taylor, reference evapotranspiration, and pan evaporation methods to estimate pasture evapotranspiration

Actual evapotranspiration (ET a) was measured at 30-min resolution over a 19-month period (September 28, 2000–April 23, 2002) from a nonirrigated pasture site in Florida, USA, using eddy correlation methods. The relative magnitude of measured ET a (about 66% of long-term annual precipitation at the study site) indicates the importance of accurate ET a estimates for water resources planning. The time and cost associated with direct measurements of ET a and the rarity of historical measurements of ET a make the use of methods relying on more easily obtainable data desirable. Several such methods (Penman–Monteith (PM), modified Priestley–Taylor (PT), reference evapotranspiration (ET 0), and pan evaporation ( E p)) were related to measured ET a using regression methods to estimate PM bulk surface conductance, PT α, ET 0 vegetation coefficient, and E p pan coefficient. The PT method, where the PT α is a function of green-leaf area index (LAI) and solar radiation, provided the best relation with ET a (standard error (SE) for daily ET a of 0.11 mm). The PM method, in which the bulk surface conductance was a function of net radiation and vapor-pressure deficit, was slightly less effective (SE=0.15 mm) than the PT method. Vegetation coefficients for the ET 0 method (SE=0.29 mm) were found to be a simple function of LAI. Pan coefficients for the E p method (SE=0.40 mm) were found to be a function of LAI and E p. Historical or future meteorological, LAI, and pan evaporation data from the study site could be used, along with the relations developed within this study, to provide estimates of ET a in the absence of direct measurements of ET a. Additionally, relations among PM, PT, and ET 0 methods and ET a can provide estimates of ET a in other, environmentally similar, pasture settings for which meteorological and LAI data can be obtained or estimated.

Estimating long-term annual precipitation in a mountainous region from a diagnostic model

Much of New Zealand's precipitation is modulated by windflow over its orography. Rain-gauge networks are normally sparse, and because measurement programmes are relatively expensive, there are considerable benefits in modelling and mapping spatial patterns of precipitation in order to provide information at sites where no data exists. In this paper a simple, numerically robust diagnostic model (VDEL) for estimating orographic precipitation is used to estimate annual precipitation normals for a mountainous region of the southern North Island, New Zealand. The VDEL model, developed initially to analyse storm precipitation patterns, is based on the estimation of orographically forced vertical motion as Vs·∇Zs where ∇Zs is the height of the terrain and Vs the low-level horizontal windflow upstream of the mountain range. Precipitation patterns were diagnosed by VDEL for four main windflow directions and calibrated against annual precipitation normals by means of a multivariate regression mapping function. Areal average precipitation, estimated from catchment runoffs, was reproduced with errors in the 5 to 10 per cent range. © 1997 the Royal Meteorological Society.

Characterizing the distribution of observed precipitation and runoff over the continental United States

This paper describes the development of a comprehensive geographic database of historical precipitation and runoff measurements for the conterminous U.S. The database is used in a spatial analysis to characterize large scale precipitation and runoff patterns and to assess the utility and limitations of using historical hydro-meteorological data for providing spatially distributed precipitation estimates at regional and continental scales. Long-term annual average precipitation (P) and runoff (Q) surfaces (geographically referenced, digital representations of a continuous spatial distribution) generated from interpolation of point measurements are used in a distributed water balance calculation to check the reliability of precipitation estimates. The resulting input-output values (P- Q) illustrate the deficiency (sparse distribution and low elevation bias) of historical precipitation measurements in the mountainous western U.S. where snowmelt is an important component of the annual runoff. The incorporation of high elevation snow measurements into the precipitation record significantly improves the water balance estimates in some areas and enhances the utility of historical data for providing spatially distributed precipitation estimates in topographically diverse regions. Regions where the use of historical precipitation data may be most limited for precipitation estimation are identified and alternatives to the use of interpolated historical data for precipitation estimation across large heterogenous regions are suggested. The research establishes a database for continental scale studies and provides direction for the successful development of spatially distributed regional scale water balance models.