Annual Cumulative Precipitation Research Articles

Exploration of potential groundwater resources at Thuwal area, north of Jeddah, Saudi Arabia, using remote sensing data analysis and geophysical survey

The study uses the applications of remote sensing in analyzing the main topographic features of the study area. The digital elevation model derived from the Shuttle Radar Topography Mission (SRTM) satellite is used to devise spillway torrents and their tributaries of the different drainage basins in the study area. The digital rainfall data recorded by the Tropical Rainfall Measuring Mission (TRMM) climate research satellite is used to determine places with the highest rainfall within the different drainage basins in the area. Other satellite data (e.g. Landsat-8) are used in identifying and studying the various geological structures in the study area, which intersect the spillway torrents. Such areas may allow seizure of large quantities of water as potential, close to the surface, groundwater (Quaternary) aquifer. Areas of potential hydrological traps have been identified and marked for further geophysical (geoelectrical) surveys. The geophysical studies helped in identifying the shallow geological structures and the thickness of the subsurface sediments. It also assists in determining the size of the groundwater aquifer and the water quality within these aquifers. The study showed a decline of freshwater aquifer in Quaternary sediments. The Tertiary groundwater aquifer is the most prevalent, where this appears normal saline aquifer. All the aquifers within the study area are being recharged from Quaternary sediments by rainwater. The cumulative annual precipitation rate increases in the South-East of the study area, specifically over Wadi Khulais and significantly drops to lower rainfall rates in the rest of the region. Running water permeates the Quaternary sediments, which in turn infiltrates and recharges the Tertiary aquifer. The salinity of the latter depends mostly on the nature of its constituent rocky material.

Changes of Benthic Macroinvertebrate Community Composition Following Natural Temperature and Precipitation Increase.

To investigate the changes of dominant species of benthic macroinvertebrates according to the changes of temperature and precipitation, we surveyed twenty sites of the main Seomjin River in May and September in 2013 and 2014. The temperature, precipitation, water quality factors and substrate composition, which are important factors in benthos habitat environment, were collected and measured. The average temperature of the Seomjin River increased by 0.2℃ in 2014 compared to 2013, and the temperature increased from upstream to downstream, showing a difference of more than 3℃. Also, the annual cumulative precipitation (ACP) was increased toward low latitude. The temperature of Seomjin River increased more than twice in September (21.7~24.5℃) after rainfall compared to May (7.6~11.3℃) before rainfall, and CP (cumulative precipitation) increased about 3 times before rainfall (263 mm~287.5 mm) and after rainfall (756.3mm~882 mm). Due to washing effect by summer precipitation, total number of species and individuals for benthic macroinvertebrates were higher in May than in September. Chironomidae sp. and Choroterpes altioculus were dominated in May, Ecdyonurus levis, Macrostemum radiatum and Choroterpes altioculus were dominated in September. As a result of correlation analysis between community indices and environment factors, it was found that there is a high correlation with boulder and sand among substrate compositions. According to the results of cluster analysis based on temperature, CP and the dominant species of benthic macroinvertebrates in Seomjin River, it was divided into two groups following temperature and CP, and the dominant species and geographical position were reflected and divided into detailed groups.

EFFECT OF CLIMATE CHANGE ON GROUNDWATER AND SALTS STORAGE IN EL SHEIKH ZUWAID-RAFAH, NORTH SINAI, EGYPT

Identifying and quantifying future climate impacts on water resources has major economic and societal implications, rendering such studies extremely important for water planners. In this research, we integrate the outputs of the general global models GDFL-ESM2M (the suitable one of the three studied models; CNRM-CM5, GFDL-ESM2M and EC-EARTH) downscaled by regional climate model (RCA4) under representative concentration pathways RCPs scenarios 8.5, into two hydrological models to provide approximations of climate change impacts on water quantity and quality in El Sheikh Zuwaid-Rafah quaternary aquifer system which is the main source of water in the area. The projected changes of the rising scenario between the periods 1980-2005 and 2050-2075 from the three studied GCMs predicted an increase in the mean of July temperature between 4.2 - 4.8 K (kelvin degree), whereas January temperature was estimated to increase between 1.8 - 5.4 K (kelvin degree). The cumulative annual precipitation was estimated to decrease by a range varied between 30% to 51%. A Simple Bias correction (SBC) technique was implemented to correct the simulated monthly precipitation series of RCA4 (GDFL-ESM2M) over Sinai Peninsula. A three dimensional finite difference flow model (Processing MODFLOW -PM5), and the implemented solute transport model (MT3D) were used to predict the groundwater and the total dissolved solids storage. Results from running the raising scenario RCP 8.5 estimated that by the hydrological year 2074 groundwater recharge would be decreased by 2.73 M.m3, leading with the yearly exploitation to decrease groundwater storage to 11.83 M.m3 and decrease in dissolve salt storage 33.1 M. Kg.

辽河三角洲滨海湿地气候变化分析

利用辽河三角洲滨海湿地及周边旱地气象站1961~2012年的逐月地面观测资料，对比分析了温度、湿度、降水量、蒸发等气象要素变化。应用Mann-Kendall法对变化趋势和突变进行了分析。结果表明：近52a来辽河三角洲滨海湿地的平均气温表现明显上升趋势，倾向率为0.31℃/10a，突变时间在1988年，蒸发量表现明显下降趋势，倾向率为55 mm/10a，突变时间在1986年，相对湿度和降水量表现为上升，趋势不显著。湿地气候存在比旱地更高的增暖趋势，湿地年平均气温9.11℃，月平均温度大于周边旱地，尤其是在冬季能减缓气温降低；湿地年平均相对湿度66%，在生长季小于旱地，增湿作用主要体现在冬季；湿地年降水量643.88 mm，比旱地高26.95 mm，主要集中在7~9月份；湿地年蒸发量1540 mm，比旱地低74 mm。 Based on the meteorological observation data from 1961 to 2012 in Liaohe delta coastal wetland, we compare and analyze the meteorological elements such as the atmospheric temperature, an-nual humidity, precipitation, evaporation between wetland and dry land. Mann-Kendall test tech-nique is applied to analyze the trend and jump change. The results show that the annual average temperature increased obviously with the rate 0.31˚C/10a over the past 52 years, while the jump change appeared in 1988; The annual average cumulative evaporation decreased obviously with the rate 55 mm/10a, while the jump change appeared in 1986, their relative humidity and cumulative precipitation increasing performance were not significant. The warming trend of wetland climate is higher than that of the surrounding dry land. The annual average temperature of wetlands is 9.11˚C, the monthly average temperature is greater than the surrounding dry land, and the wetland can slow down the environment temperature change greater than the surrounding dry land, especially in winter. The annual average relative humidity of wetland is 66%, it is less than the dry land in growing season, humidifying function mainly reflects in winter. Annual cumulative precipitation of wetland is 643.88 mm, which is 26.95 mm higher than dry land, and the phenomenon is more obvious from July to September. Annual cumulative evaporation of wetland is 1540 mm, which is 74 mm lower than dry land.

Environmental drivers of decadal change of a mangrove forest in the North coast of the Yucatan peninsula, Mexico

Mangrove forests provide important ecosystem services, but are under constant pressure from natural, anthropogenic, and climate change related disturbances. Environmental drivers on mangrove change at large spatial scales, other than sea level rise, are not well understood. In here, we use spatially explicit methods to identify the main environmental drivers of mangrove coverage change over a decade in the landscape of the North coast of the Yucatan peninsula, Mexico. A post-supervised classification approach on seven SPOT 5 multispectral satellite images was used to construct thematic maps of mangrove coverage between 2004 and 2014. A linear regression model between the thematic maps was performed to estimate the mangrove coverage change rate per pixel. Climate surfaces for annual maximum, minimum and mean temperature, and annual mean and cumulative precipitation for the region were calculated for the period 1980–2009 using data obtained from the National Meteorological Service. The effect of environmental variables on mangrove coverage change rates was assessed with a boosted generalized additive model (boosted GAM). The lowest and highest overall accuracy obtained for the time series thematic maps were 87.14% (Kappa = 0.78), and 97.5% (Kappa = 0.95), respectively. The most influential environmental variables on mangrove coverage change were annual cumulative precipitation (21%), and annual maximum temperature (9%). Current climate change scenarios for the region predict an increase in temperature and a decrease in precipitation, intensifying environmental stress on this ecosystem. Therefore, adequate management strategies are fundamental to help maintain the mangrove forest under changing environmental conditions.

Climate variability, farmland value, and farmers’ perceptions of climate change: implications for adaptation in rural Pakistan

ABSTRACTMany studies have examined the impact of climatic variability on agricultural productivity, although an understanding of these effects on farmland values and their relationship to farmers’ decisions to adapt and modify their land-use practices remains nascent in developing nations. We estimated the impacts of the deviation in our study year's (2012) temperature and precipitation patterns from medium-term (1980–2011) climatic patterns on farmland values in Pakistan. This was accomplished by employing a modified form of a Ricardian regression model. We also examined farmers’ perceptions of climate change during this period, as well as their perceptions of climate change impacts on farm productivity, in addition to past and anticipated farm adaptation strategies. Our results indicate that positive temperature deviation from the medium-term mean – indicative of climatic change – affects farmland values in Pakistan. Deviation in annual cumulative precipitation conversely appears to have no significant impact. Estimates of the marginal impact of temperature deviation suggested a slight but negative linear relationship with farmland values. The location of farms in areas where farmers can avail financial or extension services conversely had a positive impact on farmland values, as did the availability of irrigation facilities. Our analysis of farmers’ perceptions of climate change and their consequent adaptation behavior indicated a relatively high degree of awareness of climatic variability that influenced a number of proactive and future anticipated farm adaptation strategies. Examples included increased use of irrigation and farm enterprise diversification, as well as land-use change, including shifting from agriculture into alternative land uses. National policy in Pakistan underscores the importance of maintaining a productive rural agricultural sector. Our findings consequently highlight the importance of appropriate adaptation strategies to maintain both farm productivity and farmland values in much of Pakistan. The implications of increased extension and financial services to enhance farmers’ potential for climate change adaptation are discussed.

Effects of harvesting and drought on CO2and H2O fluxes in an aspen-dominated western boreal plain forest: early chronosequence recovery

This study examines the hydrological recovery of two regenerating boreal trembling aspen (Populus tremuloides Michx.) dominated stands and the sensitivity of that regeneration to drought within the first 5 years of establishment. The results indicate that evapotranspiration fluxes and water-use efficiency rebounded quickly as a result of new vegetation foliage growth and wet conditions found within the first 2 years following the harvest. However, a period of dry years had a significant influence on rates of postharvest growth, carbon dioxide (CO2), and water fluxes at these sites. The northern study area (NSA) and southern study area (SSA) were harvested in the winters of 2007 and 2008, respectively. The first and second years of regeneration at the SSA and NSA, respectively, were marked by an early spring thaw and higher-than-normal precipitation, while air temperatures remained slightly above the 30-year normal. During this period, mean measured height of vegetation tripled at both sites, and cumulative evapotranspiration was approximately 60% of that prior to harvest by the end of the second year of growth. By the third year (2009), the NSA became a sink for atmospheric CO2during the snow free season (days of the year 128–238) despite low precipitation during the latter half of the summer. Volumetric soil moisture content in 2009 was the highest (on average) of the 5 years examined due to heavy snowfall and a late start to the growing season (where air temperatures consistently exceeded 0 °C), resulting in sustained productivity. However, cumulative annual precipitation also declined to 79% and 57% in 2009 and 2010, respectively, of the 30-year normal for that region, leading to significant (lagged) declines in forest productivity at the NSA in 2010 and 2011. This resulted in the site becoming a source of CO2to the atmosphere during the 2010 and 2011 growing seasons (annual balance was not measured). Throughout the drought period (2009, 2010, and 2011), mean stand height increased by only 15%, 11%, and 14%, respectively, compared with the mean stand height in 2008. Water-use efficiency also declined in 2010 and 2011, whereas differences in light-use efficiency did not vary significantly because foliage was maintained (i.e., leaves did not abscise as a result of drought). The results of this study indicate that regenerating aspen stands are sensitive to drought and respond relatively quickly to changes in the soil moisture regime. This is important because regional drying as a result of predicted climatic changes combined with increased industrial activity may result in significant decline in productivity within these stands over broad regions.

Association of Seasonal Climate Variability and Age-Specific Mortality in Northern Sweden before the Onset of Industrialization

Background and aims: Little is known about health impacts of climate in pre-industrial societies. We used historical data to investigate the association of temperature and precipitation with total and age-specific mortality in Skellefteå, northern Sweden, between 1749 and 1859. Methods: We retrieved digitized aggregated population data of the Skellefteå parish, and monthly temperature and precipitation measures. A generalized linear model was established for year to year variability in deaths by annual and seasonal average temperature and cumulative precipitation using a negative binomial function, accounting for long-term trends in population size. The final full model included temperature and precipitation of all four seasons simultaneously. Relative risks (RR) with 95% confidence intervals (CI) were calculated for total, sex- and age-specific mortality. Results: In the full model, only autumn precipitation proved statistically significant (RR 1.02; CI 1.00–1.03, per 1cm increase of autumn precipitation), while winter temperature (RR 0.98; CI 0.95–1.00, per 1 °C increase in temperature) and spring precipitation (RR 0.98; CI 0.97–1.00 per 1 cm increase in precipitation) approached significance. Similar effects were observed for men and women. The impact of climate variability on mortality was strongest in children aged 3–9, and partly also in older children. Infants, on the other hand, appeared to be less affected by unfavourable climate conditions. Conclusions: In this pre-industrial rural region in northern Sweden, higher levels of rain during the autumn increased the annual number of deaths. Harvest quality might be one critical factor in the causal pathway, affecting nutritional status and susceptibility to infectious diseases. Autumn rain probably also contributed to the spread of air-borne diseases in crowded living conditions. Children beyond infancy appeared most vulnerable to climate impacts.

Spatially-explicit modelling of grassland classes – an improved method of integrating a climate-based classification model with interpolated climate surfaces

Spatially-explicit modelling of grassland classes is important to site-specific planning for improving grassland and environmental management over large areas. In this study, a climate-based grassland classification model, the Comprehensive and Sequential Classification System (CSCS) was integrated with spatially interpolated climate data to classify grassland in Gansu province, China. The study area is characterised by complex topographic features imposed by plateaus, high mountains, basins and deserts. To improve the quality of the interpolated climate data and the quality of the spatial classification over this complex topography, three linear regression methods, namely an analytic method based on multiple regression and residues (AMMRR), a modification of the AMMRR method through adding the effect of slope and aspect to the interpolation analysis (M-AMMRR) and a method which replaces the inverse distance-weighted approach for residue interpolation in M-AMMRR with an ordinary kriging approach (I-AMMRR), for interpolating climate variables were evaluated. The interpolation outcomes from the best interpolation method were then used in the CSCS model to classify the grassland in the study area. Climate variables interpolated included the annual cumulative temperature and annual total precipitation. The results indicated that the AMMRR and M-AMMRR methods generated acceptable climate surfaces but the best model fit and cross validation result were achieved by the I-AMMRR method. Twenty-six grassland classes were classified for the study area. The four grassland vegetation classes that covered more than half of the total study area were ‘cool temperate-arid temperate zonal semi-desert’, ‘cool temperate-humid forest steppe and deciduous broad-leaved forest’, ‘temperate-extra-arid temperate zonal desert’, and ‘frigid per-humid rain tundra and alpine meadow’. The vegetation classification map generated in this study provides spatial information on the locations and extents of the different grassland classes. This information can be used to facilitate government agencies’ decision-making in land-use planning and environmental management, and for vegetation and biodiversity conservation. The information can also be used to assist land managers in the estimation of safe carrying capacities, which will help to prevent overgrazing and land degradation.

Impacts of Climate Change on Extreme Precipitation Events Over Flamingo Tropicana Watershed1

Abstract: Climate change, particularly the projected changes to precipitation patterns, is likely to affect runoff both regionally and temporally. Extreme rainfall events are expected to become more intense in the future in arid urban areas and this will likely lead to higher streamflow. Through hydrological modeling, this article simulates an urban basin response to the most intense storm under anthropogenic climate change conditions. This study performs an event‐based simulation for shorter duration storms in the Flamingo Tropicana (FT) watershed in Las Vegas, Nevada. An extreme storm, defined as a 100‐year return period storm, is selected from historical records and perturbed to future climatic conditions with respect to multimodel multiscenario (A1B, A2, B1) bias corrected and spatially disaggregated data from the World Climate Research Programme's (WCRP's) database. The cumulative annual precipitation for each 30‐year period shows a continuous decrease from 2011 to 2099; however, the summer convective storms, which are considered as extreme storms for the study area, are expected to be more intense in future. Extreme storm events show larger changes in streamflow under different climate scenarios and time periods. The simulated peak streamflow and total runoff volume shows an increase from 40% to more than 150% (during 2041‐2099) for different climate scenarios. This type of analysis can help evaluate the vulnerability of existing flood control system and flood control policies.

Spatiotemporal Patterns of Production Can Be Used to Detect State Change Across an Arid Landscape

Methods to detect and quantify shifts in the state of ecosystems are increasingly important as global change drivers push more systems toward thresholds of change. Temporal relationships between precipitation and aboveground net primary production (ANPP) have been studied extensively in arid and semiarid ecosystems, but rarely has spatial variation in these relationships been investigated at a landscape scale, and rarely has such information been viewed as a resource for mapping the distribution of different ecological states. We examined the broad-scale effects of a shift from grassland to shrubland states on spatiotemporal patterns of remotely sensed ANPP proxies in the northern Chihuahuan Desert. We found that the normalized difference vegetation index (NDVI), when averaged across an eight-year period, did not vary significantly between these states, despite changes in ecosystem attributes likely to influence water availability to plants. In contrast, temporal relationships between precipitation and time-integrated NDVI (NDVI-I) modeled on a per-pixel basis were sensitive to spatial variation in shrub canopy cover, a key attribute differentiating ecological states in the region. The slope of the relationship between annual NDVI-I and 2-year cumulative precipitation was negatively related to, and accounted for 71% of variation in, shrub canopy cover estimated at validation sites using high spatial resolution satellite imagery. These results suggest that remote sensing studies of temporal precipitation–NDVI relationships may be useful for deriving shrub canopy cover estimates in the region, as well as for mapping other ecological state changes characterized by shifts in long-term ANPP, plant functional type dominance, or both.

Regional climate change projections and hydrological impact analysis for a Mediterranean basin in Southern Italy

A number of future water availability scenarios in the Crati River Basin (Southern Italy) are made by applying the outputs of three Regional Climate Models (RCMs) RegCM, HIRHAM and COSMO-CLM to the newly developed Intermediate Space Time Resolution Hydrological Model (In-STRHyM). In-STRHyM is a fully distributed hydrological model detailed enough to describe the hydrological processes of several small-medium sized Mediterranean basins. It has a relatively simple structure and is suitable for long period simulations to be undertaken within acceptable time frames. The analysis was performed using two time slices (1961–1990 and 2070–2099) with the SRES A2 (HAD3AM) and A1B (ECHAM5/MPI-OM) scenarios. Observed biases in simulated precipitation and temperature fields during the control period (1961–1990) were corrected before using meteorological outputs from each RCM as input for In-STRHyM. A sensitivity analysis is used to help verify this procedure. While hydrological model simulations are based on different greenhouse gas emission scenarios, GCMs, RCMs and bias correction parameters and hence show noticeable differences, they all agree on a general reduction in future water resource availability. An increase in the average annual temperature between +3.5 °C and +3.9 °C and a decrease between −9% and −21% in the cumulative annual precipitation are projected, leading to a drastic reduction in snow accumulation of between −82% and −92%. Evapotranspiration is expected to increase in the wintertime and decrease in summertime, with the water stress period increasing on average by 15 days. Mean annual reductions are predicted for root zone soil moisture (between −12.8 ± 1.9% and −20.7 ± 1.9%, with reductions reaching −37.7 ± 2.4% during summer), groundwater storage (−6.5 ± 1.4% and −11.6 ± 1.6%), surface runoff (−25.4 ± 6.0% and −41.2 ± 5.0%) and a significant increase in runoff variability.

Population Demographics and Dynamics of Colonizing Elk in a Desert Grassland–Scrubland

AbstractElk Cervus elaphus are rare in Southwestern desert grassland and desert-scrub habitats, and these habitats are anecdotally considered unsuitable for elk. We studied a colonizing herd in a Southwestern desert grassland–scrubland in northwestern New Mexico to determine the condition and population dynamics of elk in this habitat type. We radiotracked ≤ 24 adult (1.5 y and older) cows and ≤ 8 calves annually, 2003–2006; the sample of radiocollared cows in this study was very close to a census of the entire population for 2004–2006 based on repeated surveys and monitoring. Mean body fat of lactating cows in autumn was 10.6–13.2% in 2003–2004, indicating that lactating elk were acquiring high moderate–low good nutrition, but dropped to 5.6% in 2005 and 6.8% in 2006, indicating poor nutrition for these years of low precipitation. We found adult female survival of 0.94–1.00 and calf survival of 0.38–1.00. Calf survival was related to maternal size, maternal condition, and cumulative annual precipitation through parturition; all calf mortality occurred at or near parturition. Pregnancy rates averaged 0.33 for yearling cows and 0.86 for ≥ 2.5-y-olds, 2003–2006, and pregnancy was positively related to body mass for ≥ 2.5-y-old adults. Lactation rates of ≥ 2.5-y-olds averaged 0.59, 2003–2005, but dropped to 0.30 in 2006, due to poor maternal condition and low precipitation. Since colonization, elk have increased from about 20 to ≥ 53 individuals, a mean rate of increase of 18%/y prior to 2006, but decreasing to ≤ 4% in 2006. The high sustained rate of increase (with few exceptions) indicates that desert grassland–scrubland habitats are suitable for elk and merit consideration in elk management plans of Southwestern agencies.

Levels of the Organophosphorus Pesticide Diazinon in the Chollas Creek Watershed, San Diego CA, since Its Phase-Out in 2004

Abstract In 2004, the organophosphorus pesticide, diazinon, was phased-out for all residential uses in the United States. The objective of this study was to determine the temporal trend of diazinon levels in the Chollas Creek, CA watershed since the phase-out of this pesticide. Stormwater samples from Chollas Creek were collected during seven storm events in 2006–2007. The median diazinon level for all samples was 0.13 µg/L. Statistical analysis using the Kruskal-Wallis test revealed no statistically significant (p=0.765) spatial difference among any of the sampling sites. Correlational analysis (using the Spearman's rho test) revealed that there was no significant association between antecedent dry days and median diazinon levels (p=0.383, rho=0.393). Additionally, no association between storm event precipitation (p=0.355, rho=−0.414), median storm event intensity (p=0.585, rho=−0.252), or annual cumulative precipitation (p=0.760, rho=0.143) was observed. Trend analysis of diazinon levels (1998–2005) sho...

Influence of Vegetal Moisture Content and Nest Fate on Timing of Female Sage Grouse Migration

Many North American Tetraoninae exhibit migratory behavior (Hoffman and Braun 1975, Herzog and Keppie 1980, Cade and Hoffman 1993, Schroeder and Braun 1993), either as partial (only some individuals migrate) or differential (age or sex classes differ in timing and/ or distance) migrants between seasonal habitats (Terrill and Able 1988). Tetraoninae may migrate because of elevational or seasonal differences in habitat availability and selection, or fidelity to seasonal-use areas (Herzog and Keppie 1980, Schroeder and Braun 1993), and these migrations are typically 16 km were uncommon), allowing most individuals to find required habitats within a relatively small annual range. In contrast, the ecology of migratory populations is more complex because individuals must cope with long-distance movements to suitable seasonal ranges (Dalke et al. 1963, Berry and Eng 1985, Connelly et al. 1988, Wakkinen 1990). Although Sage Grouse do not undertake migrations at a scale similar to some avian species such as Anseriformes (Bellrose 1980), Neotropical migratory Passeriformes (Finch and Stangel 1993), or Charadriiformes (Krementz et al. 1994), their movements still m et most ecological definitions of migration (e.g., Sinclair 1983). Connelly et al. (1988), Wakkinen (1990), and Roberts n (1991) investigated the ecology of a migratory Sage Grouse population inhabiting a xeric environment (< 25 cm annual precipitation) in southeastern Idaho. Grouse used contiguous areas for wintering, breeding, and nesting but moved as far as 82 km to summer range at either higher or lower elevations. Grouse return to winter range beginning in late fall (Robertson 1991). Movements to summer range presumably occur because Sage Grouse breeding and nesti g ranges lack mesic habitats, such as wet meadows and iparian areas, that provide succulent vegetal foods for birds throughout summer (Autenrieth 1981, Connelly et al. 1988). Although reports of distance moved from breeding to summer ranges are common, little information regarding relationships between timing of thes movements and vegetal characteristics or environmental factors are available. Nest fate also may influence the ability of females to initiate migration to summer range because successful females may delay migration (Schroeder and Braun 1993). Migratory birds may rely on exogenous (environmental) factors (Terrill 1990), endogenous circannual rhythms (Berthold 1990, Gwinner 1990), or a combination of both (Krementz et al. 1994) for migrational timing cues. Sage Grouse appear to initiate migration to summer range at different times within and among years (Connelly et al. 1988), suggesting the cue for migrational timing may be influenced by exogenous factors. However, no empirical data exist to document timing and progression of plant desiccation, how weather variables might influence desiccation, or how migrational timing may be influenced by plant moisture content. We hypothesized that (1) cumulative annual precipitation and temperature influence timing of spring and summer vegetal desiccation, (2) vegetal moisture content would be higher in plants collected at sites used by Sage Grouse than at random sites, and (3) annual timing of Sage Grouse migration is related to vegetal moisture content and nest fate. 1 Received 15 February 1996. Accepted 24 July 1996. 2 Present address: U.S. Army Corps of Engineers, Waterways Experiment Station, Environmental Laboratory, 3909 Halls Ferry Rd., Vicksburg, MS 39180, e-mail: fischer@ex 1 .wes.army.mil

Epidemics of Phymatotrichum root rot (Phymatotrichum omnivorum) in cotton: environmental correlates of final incidence and forecasting criteria

SUMMARYEpidemics of Phymatotrichum root rot (PRR), caused by Phymatotrichum omnivorum, in cotton were monitored in field plots at the Blackland Research Center, Temple, Texas during the years 1969–1982. In most years disease incidence, assessed at periodic intervals during the growing season, increased smoothly and levelled off at values in the range 0–04‐0‐99 (proportion of plants killed). During two years there were marked increases in PRR late in the growing season. Increments in PRR were associated with preceding increments in precipitation but only when the latter were large. The final incidence of PRR late in August was directly related (in all but one of the 14 years) to cumulative precipitation in the range 36–100 cm, and inversely related (in all 14 years) to air temperatures greater than 34 oC. Regression was used to relate final PRR incidence to derived weather variates but the equations obtained did not provide a realistic basis for forecasting: the best predictive variates included cumulative precipitation up to mid‐August. A threshold criterion given by P/T &gt; 1·45, where P was cumulative precipitation (cm) from 1 January and T was the mean maximum temperature (°C) during the preceding 10 days, was derived. This criterion satisfactorily grouped years with high (&gt;0·;50) and low (&lt;0–50) incidences of PRR. In those years where a forecast of high incidence was made, the criterion was satisfied prior to the first appearance of PRR (mid‐June); where a forecast of low incidence was made, the criterion was not satisfied until late August. The forecasting criterion was evaluated at three sites in the Blacklands region in 1983, at two in 1984, and at Temple only in 1985. In 1983 and 1984, final PRR incidences of less than 0–50 were forecast and observed; in 1985, cumulative annual precipitation exceeded 50 cm by early June, the threshold criterion was satisfied prior to the first observation of symptoms, and PRR incidence was 0–80 late in August.