Changes In Annual Rainfall Research Articles

Use of CLIGEN to Simulate Climate Change in Southeastern Australia

CLIGEN is a stochastic weather generator to reproduce, statistically, daily weather variables, and CLIGEN output has been used to simulate the impact of climate change on runoff and soil erosion. Weather observations from regions with significant climate variability and change could be used to determine how to manipulate the input to or output from CLIGEN to simulate climate change scenarios. Previous studies mostly used simplistic approaches, such as changing the average daily rainfall on wet days by a fixed percentage or multiplying the CLIGEN-generated daily rainfall by a fixed factor. The aim of this article is to develop a method based on available historical data to adjust CLIGEN parameter values when, historically, rainfall has significantly changed. In southeastern Australia, rainfall showed a significant and abrupt increase in a 30-year period since the late 1940s from the preceding three decades. However, rainfall has decreased since the late 1970s, significantly at many sites in the same region. Long-term (90 years) daily rainfall data from 30 sites in this region were used to examine decadal variations in rainfall and to evaluate the changes to CLIGEN parameter values with significant changes in annual rainfall. Average daily rainfall, standard deviations, skewness coefficients, and probabilities of a wet day following a wet day and a wet day following a dry day were analyzed for each of three 30-year periods and for each of 30 sites in southeastern Australia. This article shows that rainfall data for the period from 1919 to 1978 would suggest an increase in rainfall in southeastern Australia. However, from the perspective of the period from 1949 to 2008, the conclusion of decreasing rainfall would be reached. Both these 60-year periods broadly coincide with an underlying trend of increased temperature in Australia and globally. Daily rainfall data for the 90-year period show that there are strong positive correlations between changes in mean monthly rainfall and changes in mean daily rainfall, standard deviation, and the probability of wet-following-dry sequences. There is little evidence to suggest ways of adjusting skewness coefficients or wet-following-wet probabilities to simulate changes in mean monthly rainfall for this region. A set of regression equations was developed to allow easy adjustment of CLIGEN parameter values to simulate monthly rainfall change for both increasing and decreasing rainfall change scenarios. The results show that when CLIGEN parameter values were adjusted using changes in monthly rainfalls and regional relationships for the three important parameter values, output from CLIGEN was able to reproduce the changes in rainfall when compared with historical observations. The proposed methodology for adjusting CLIGEN parameters is not site-specific and could also be used for other similar regions in the world.

Daily distribution Map of Ozone (O3) from AIRS over Southeast Asia

Problem statement: Daily retrieved Ozone (O3) column data for 12 day for periods varying (11-18 August) 2005 and 2003 and (12-19 February) 2005, obtained from the Atmospheric Infrared Sounder AIRS, are utilized to investigate the ozone distribution over the Southeast Asia. Approach: AIRS included on the Earth Observing System (EOS) Aqua satellite launched on 4 May 2002. Ozone (O3) is the gas that naturally present in our atmosphere and is a critical atmospheric trace species in the stratosphere and troposphere. Most ozone resides in the stratosphere. Ozone can be “good” or “bad” for your health and the environment. Closer to Earth, in the air we breathe, Ozone is a harmful pollutant that causes damage to lung tissue and plants; it is a major constituent of smog. Results: The aim of this study was to investigate Daily Distribution map and Indonesia forest fires influences on O3 over Peninsular Malaysia and Thailand. The land use map of the study area was conducted by using total column O3 obtained from AIRS/Aqua Level 3 Daily (AIRX3STD) 1×1° spatial resolution ascending Standard, are used to study the O3 distribution and the impact of Indonesia forest fire. Considerable variations demonstrate annual changes in rainfall and drought patterns in various seasons (dry and wet season). Note such variations in the Ozone emissions over study area, while highest O3 occurs over Industrial, congested urban zones and existence of Swamps and lakes during dry season and a greater draw down of O3 occurs in the pristine marine environment over Surat Thani during wet seasons. Conclusion/Recommendations: In particular, we observe a quasi-biennial variation in O3 emissions from study area with two contrary cases, the higher concentrations around the equatorial regions at dry season and less at wet season. Examining satellite measurements, we find the enhanced O3 emission correlates with occasions of less rainfall during dry season.

Recent Changes in Annual Rainfall over Southern Taif Province, Saudi Arabia

Recent Changes in Annual Rainfall over Southern Taif Province, Saudi Arabia

Spatial and temporal characteristics of the annual rainfall frequency distribution in Cyprus

This study is a statistical analysis of the time series of rainfall-recording stations in Cyprus. The aim of this analysis is the better appreciation of the spatio-temporal changes of annual rainfall. For the needs of the present study, the Gamma distribution was fitted to the rainfall records. The characteristics of this distribution were determined for each of the thirty-year periods that are consecutively formed in the time period spanning from 1917 to 2006. The results have shown that there exists a distinct temporal and spatial change of the annual rainfall amounts, as they can be determined by the characteristics of the distribution that was utilized.

Crassulacean acid metabolism under global climate change

Crassulacean acid metabolism under global climate change

Response of hydrological processes to land‐cover and climate changes in Kejie watershed, south‐west China

AbstractLand‐cover/climate changes and their impacts on hydrological processes are of widespread concern and a great challenge to researchers and policy makers. Kejie Watershed in the Salween River Basin in Yunnan, south‐west China, has been reforested extensively during the past two decades. In terms of climate change, there has been a marked increase in temperature. The impact of these changes on hydrological processes required investigation: hence, this paper assesses aspects of changes in land cover and climate. The response of hydrological processes to land‐cover/climate changes was examined using the Soil and Water Assessment Tool (SWAT) and impacts of single factor, land‐use/climate change on hydrological processes were differentiated. Land‐cover maps revealed extensive reforestation at the expense of grassland, cropland, and barren land. A significant monotonic trend and noticeable changes had occurred in annual temperature over the long term. Long‐term changes in annual rainfall and streamflow were weak; and changes in monthly rainfall (May, June, July, and September) were apparent. Hydrological simulations showed that the impact of climate change on surface water, baseflow, and streamflow was offset by the impact of land‐cover change. Seasonal variation in streamflow was influenced by seasonal variation in rainfall. The earlier onset of monsoon and the variability of rainfall resulted in extreme monthly streamflow. Land‐cover change played a dominant role in mean annual values; seasonal variation in surface water and streamflow was influenced mainly by seasonal variation in rainfall; and land‐cover change played a regulating role in this. Surface water is more sensitive to land‐cover change and climate change: an increase in surface water in September and May due to increased rainfall was offset by a decrease in surface water due to land‐cover change. A decrease in baseflow caused by changes in rainfall and temperature was offset by an increase in baseflow due to land‐cover change. Copyright © 2009 John Wiley & Sons, Ltd.

A revised picture of the structure of the “monsoon” and land ITCZ over West Africa

This article presents an overview of the land ITCZ (Intertropical Convergence Zone) over West Africa, based on analysis of NCAR–NCEP Reanalysis data. The picture that emerges is much different than the classic one. The most important feature is that the ITCZ is effectively independent of the system that produces most of the rainfall. Rainfall linked directly to this zone of surface convergence generally affects only the southern Sahara and the northern-most Sahel, and only in abnormally wet years in the region. A second feature is that the rainbelt normally assumed to represent the ITCZ is instead produced by a large core of ascent lying between the African Easterly Jet and the Tropical Easterly Jet. This region corresponds to the southern track of African Easterly Waves, which distribute the rainfall. This finding underscores the need to distinguish between the ITCZ and the feature better termed the “tropical rainbelt”. The latter is conventionally but improperly used in remote sensing studies to denote the surface ITCZ over West Africa. The new picture also suggests that the moisture available for convection is strongly coupled to the strength of the uplift, which in turn is controlled by the characteristics of the African Easterly Jet and Tropical Easterly Jet, rather than by moisture convergence. This new picture also includes a circulation feature not generally considered in most analyses of the region. This feature, a low-level westerly jet termed the African Westerly Jet, plays a significant role in interannual and multidecadal variability in the Sahel region of West Africa. Included are discussions of the how this new view relates to other aspects of West Africa meteorology, such as moisture sources, rainfall production and forecasting, desertification, climate monitoring, hurricanes and interannual variability. The West African monsoon is also related to a new paradigm for examining the interannual variability of rainfall over West Africa, one that relates changes in annual rainfall to changes in either the intensity of the rainbelt or north–south displacements of this feature. The new view presented here is consistent with a plethora of research on the synoptic and dynamic aspects of the African Easterly Waves, the disturbances that are linked to rainfall over West Africa and spawn hurricanes over the Atlantic, and with our knowledge of the prevailing synoptic and dynamic features. This article demonstrate a new aspect of the West Africa monsoon, a bimodal state, with one mode linked to dry conditions in the Sahel and the other linked to wet conditions. The switch between modes appears to be linked to an inertial instability mechanism, with the cross-equatorial pressure gradient being a critical factor. The biomodal state has been shown for the month of August only, but this month contributes most of the interannual variability. This new picture of the monsoon and interannual variability shown here appears to be relevant not only to interannual variability, but also to the multidecadal variability evidenced in the region between the 1950s and 1980s.

Climate change effects on pasture systems in south-eastern Australia

Climate change projections for Australia predict increasing temperatures, changes to rainfall patterns, and elevated atmospheric carbon dioxide (CO2) concentrations. The aims of this study were to predict plant production responses to elevated CO2 concentrations using the SGS Pasture Model and DairyMod, and then to quantify the effects of climate change scenarios for 2030 and 2070 on predicted pasture growth, species composition, and soil moisture conditions of 5 existing pasture systems in climates ranging from cool temperate to subtropical, relative to a historical baseline. Three future climate scenarios were created for each site by adjusting historical climate data according to temperature and rainfall change projections for 2030, 2070 mid- and 2070 high-emission scenarios, using output from the CSIRO Mark 3 global climate model. In the absence of other climate changes, mean annual pasture production at an elevated CO2 concentration of 550 ppm was predicted to be 24–29% higher than at 380 ppm CO2 in temperate (C3) species-dominant pastures in southern Australia, with lower mean responses in a mixed C3/C4 pasture at Barraba in northern New South Wales (17%) and in a C4 pasture at Mutdapilly in south-eastern Queensland (9%). In the future climate scenarios at the Barraba and Mutdapilly sites in subtropical and subhumid climates, respectively, where climate projections indicated warming of up to 4.4°C, with little change in annual rainfall, modelling predicted increased pasture production and a shift towards C4 species dominance. In Mediterranean, temperate, and cool temperate climates, climate change projections indicated warming of up to 3.3°C, with annual rainfall reduced by up to 28%. Under future climate scenarios at Wagga Wagga, NSW, and Ellinbank, Victoria, our study predicted increased winter and early spring pasture growth rates, but this was counteracted by a predicted shorter spring growing season, with annual pasture production higher than the baseline under the 2030 climate scenario, but reduced by up to 19% under the 2070 high scenario. In a cool temperate environment at Elliott, Tasmania, annual production was higher than the baseline in all 3 future climate scenarios, but highest in the 2070 mid scenario. At the Wagga Wagga, Ellinbank, and Elliott sites the effect of rainfall declines on pasture production was moderated by a predicted reduction in drainage below the root zone and, at Ellinbank, the use of deeper rooted plant systems was shown to be an effective adaptation to mitigate some of the effect of lower rainfall.

Climatic control of sediment yield in dry lands following climate and land cover change

Long‐term climate and short‐term environmental change both affect catchment sediment yield, yet isolating the respective contributions has been difficult. To help separate the different roles, a numerical ecogeomorphic model has been used to explore the erosional impacts of different environmental changes across a gradient of annual rainfall in water‐limited fluvial landscapes. Results demonstrate that following vegetation disturbances, sediment yield is a maximum in arid to semiarid climates, decreasing in dryer climates owing to a paucity of vegetation to disturb and in wetter climates owing to increasingly rapid postdisturbance recovery. The case of sustained changes in annual rainfall is more complicated owing to trade‐offs between changes in vegetation cover and runoff. As climates abruptly become wetter, the barren, arid landscapes produce the greatest sediment, but a secondary peak occurs in semiarid climates where a high proportional increase in runoff coincides with runoff‐limited erosion. Sediment yield drops relative to prechange conditions between these two maxima, where vegetation cover substantially increases and runoff drops. Conversely, as climates become dryer, the effects of vegetation and runoff are transposed: sediment yield peaks become troughs, and troughs become peaks. Together, these results suggest that sediment yield depends both on the nature of the disturbance and on the landscape and climatic contexts in which the disturbance acts. Prechange landscapes and climate set the stage by prescribing whether sediment yield is vegetation limited or runoff limited. Environmental changes then affect erosion by augmenting or diminishing the prevailing geomorphic limitation.

Regional Projections of Future Seasonal and Annual Changes in Rainfall and Temperature over Australia Based on Skill-Selected AR4 Models

Abstract Daily data from climate models submitted to the Fourth Assessment of the Intergovernmental Panel on Climate Change are compared with daily data from observations over Australia by measuring the overlap of the probability density functions (PDFs). The capacity of these models to simulate maximum temperature, minimum temperature, and precipitation is assessed. The resulting skill score is then used to exclude models with relatively poor skill region by region over Australia. The remaining sample of coupled climate models is then used to determine the seasonal changes in these three variables under a high- (A2) and low- (B1) emission scenario for 2050 and 2100. The authors demonstrate that some projected phenomena, such as the projected drying over southwest Western Australia, are robust and not caused by the inclusion of some weak models in earlier assessments. Some other results, such as the projected change in the monsoon, are more consistent among the good climate models. Consistent with earlier work, a consistent pattern of mean warming is identified in the projections. The amount of warming in the 99.7th percentile is not dramatically higher than the warming in the mean. However, while the mean warming is generally least in the south, the amount of warming in the 99.7th percentile is substantially higher along the southern coast of Australia. This is due to a coupling of the temperature response with reduced rainfall, which causes drying and allows extreme maximum temperatures to increase dramatically. The authors show that, in general, the amount of rainfall is projected to change relatively little, but the frequency of rainfall decreases and the intensity of rainfall at the upper tail of the distribution increases. However, the scale of the increase in extreme rainfall is not large on the time scales analyzed here. The range in projected temperature changes among those climate models with skill in simulating the observations is at least twice as large for the 99.7th/0.3rd percentiles as for the mean. For rainfall, the range among the good models is of order 10 times greater in the 99.7th percentile than in the mean. Since the impact of changes in extremes is increasingly recognized as societally important, this result strongly limits the use of climate model data to explore sectors that are vulnerable to extremes. This suggests an evaluation strategy that focuses on model capacity to simulate whole PDFs since capacity to simulate the mean is a necessary but insufficient criterion for determining a model’s value for future projection.

Estimating the sensitivity of mean annual runoff to climate change using selected hydrological models

Hydrological model sensitivity to climate change can be defined as the response of a particular hydrological model to a known quantum of climate change. This paper estimates the hydrological sensitivity, measured as the percentage change in mean annual runoff, of two lumped parameter rainfall-runoff models, SIMHYD and AWBM and an empirical model, Zhang01, to changes in rainfall and potential evaporation. These changes are estimated for 22 Australian catchments covering a range of climates, from cool temperate to tropical and moist to arid. The results show that the models display different sensitivities to both rainfall and potential evaporation changes. The SIMHYD, AWBM and Zhang01 models show mean sensitivities of 2.4%, 2.5% and 2.1% change in mean annual flow for every 1% change in mean annual rainfall, respectively. All rainfall sensitivities have a lower limit of 1.8% and show upper limits of 4.1%, 3.4% and 2.5%, respectively. The results for potential evaporation change are −0.5%, −0.8% and −1.0% for every 1% increase in mean annual potential evaporation, respectively, with changes rainfall being approximately 3–5 times more sensitive than changes in potential evaporation for each 1% change in climate. Despite these differences, the results show similar correlations for several catchment characteristics. The most significant relationship is between percent change in annual rainfall and potential evaporation to the catchment runoff coefficient. The sensitivity of both A and B factors decreases with an increasing runoff coefficient, as does the uncertainty in this relationship. The results suggest that a first-order relationship can be used to give a rough estimate of changes in runoff using estimates of change in rainfall and potential evaporation representing small to modest changes in climate. Further work will develop these methods further, by investigating other regions and changes on the subannual scale.

Caractérisation de la Variabilité Spatiale et Temporelle des Précipitations Annuelles sur le Bassin du Lac Tchad au Cours du 20ème Siècle/Spatial and Temporal Variability of Annual Rainfall in the Lake Chad Basin During the 20th Century

The study of changes in annual rainfall in the Lake Chad basin during the 20th century is based on the analysis of 47 stations, i.e. a total of about 1600 station-years for the time series with more than 25 years of data. As previously observed in western and Sahelian Africa, robust tests of shift in time series identify a significant change in mean from the beginning of the 1960s between the latitudes 11 and 13°N, and a little later in this decade for the northern stations. The analysis of decadal rainfall shows that the 1950s decade was very humid and the next three decades were drier. These dry conditions were more and more severe until the 1980s. Data available after 1990 do not show any inversion in the trend. The annual rainfall decreases from south to north, and the regional gradient has changed from 1.5 mm km−1 in the 1950s to 1.2 mm km−1 in the 1980s between the latitudes 10 and 14°N.

Daily rainfall trend in the Valencia Region of Spain

¶We have analyzed daily rainfall trends throughout the second half of the 20th century in the western Mediterranean basin (Valencia Region, E of Spain). The area is characterized by high torrentiality, and during the second half of the 20th century some of the highest daily rainfall values in the Mediterranean basin have been recorded. In this area, mean annual rainfall varies between 500 and 300 mm and is overwhelmingly dependent on just a few days of rain. Daily maximum rainfall varies on average from 120 mm day−1 to 50 mm day−1, and represents a mean of 17% (coastland) to 9% (inland) of annual rainfall. The 10 days in each year with the heaviest rainfall (called “higher events”) provide over 50% of the annual rainfall and can reach more than 400 mm on average. We compared the annual rainfall trend and the trend of higher and minor events defined by percentiles, both in volume and variability. We, therefore, tested whether annual rainfall changes depend on the trend of the higher (rainfall) events. To overlap spatial distribution of trends (i.e.: positive, no significant and negative trends) we have used cross-tab analysis. The results confirm the hypothesis that annual rainfall changes depend on changes found in just a few rainy events. Furthermore, in spite of their negative trend, higher events have increased their contribution to annual rainfall. As a consequence, although torrential events may have diminished in magnitude, future scenarios seem to be controlled by a limited number of rainy events which will become more and more variable year on year. The high spatial density of data used in this work, (97 observatories per 24.000 km2, overall mean 1 observatory per 200 km2), suggests to us that extreme caution should be applied when analyzing regional and sub-regional changes in rainfall using GCM output, especially in areas of high torrentiality.

Trend analysis of land use change effect on discharge in the Chao Phraya river basin

Local scientists and engineers in Thailand have recognized and pointed out a decreasing trend in discharge in the Chao Phraya river in recent years. However, no solid data or analysis to show a decline has been reported. This study is to find trends in river discharge data and to analyze significant causes of the trend. The following results were obtained:(1) As a result of examining discharge at 10 gauging stations in the Chao Phraya river basin, the significant decline of the annual discharge is found at 8 stations out of the ten;(2) 17 out of 18 sub-basins of the Chao Phraya river basin have no tendency in annual rainfall change, but the only one sub-basin in the upper Yom river basin has tendency of declining rainfall according to the Kendall rank test at 95% significance level;(3) and it is considered that major cause of the discharge decline is a change of the land use to cropland such as the orchard from paddy field rather than rainfall.

Water quantity and quality as the factors driving the Serengeti ecosystem, Tanzania

Thirty nine years of rainfall data from 232 sites, 5 years of river discharge data from 3 rivers, 4 years of animal migration data and 4 years of water quality data at 60 sites were explored to quantify the role of water in the Serengeti ecosystem. Seasonal variations in rainfall are largely predictable; interannual fluctuations are huge and not predictable solely from the Southern Oscillation Index. The wildebeest and zebras start their annual migration at the end of the wet season well before surface water runs out, however these waters are very saline (salinity ≈ 5–17 psu). The timing of the migration appears predictable from a salinity model. Salinity is also important for the vegetation because high salinity coincides with the transition between wooded savanna and grassland. This transition has moved markedly southward in the last 30 years, this change may be due to decadal changes in annual rainfall. Most rivers are commonly ponded, with ponds having a flushing rate of 1 month in the wet season and zero flushing in the dry season. These ponds form the only source of water for wildlife for several months a year. The water quality varies spatially and temporally. pH values vary between 5.9 and 10 and are correlated with salinity. Surface waters are heavily eutrophicated from animal dung. As a result, the dissolved oxygen concentration near the surface fluctuates widely between 1 and 200% of saturation. Direct solar heating is restricted to the top few cm because of low visibility. A strong thermal stratification in temperature (2 °C/m) results and inhibits aeration. Bottom waters can be anoxic and are aerated only when hippopotamus stir the water. Poor water quality may affect wildlife health and production.

Are Namibia's Grasslands Desertifying?

We compared the herbage standing crop on 31 farms along a rainfall gradient in Namibia (southwestern Africa) in 1997 with the results attained for the same gradient by Walter (1939). We found that the slope for the regression of herbage yield on mean annual rainfall in 1997 was 5.93, i.e. 5.93 kg herbage was produced per hectare for every 1 mm increase in rainfall along the gradient. This regression slope is considerably lower than that in Walter's (1939) study (slope = 10.34). Thus, current grassland productivity per unit of rainfall in Namibia is about half that of 50 years ago. There is no evidence of a change in annual rainfall over this period, nor is there any evidence that either short-term (current) or longer-term (11 years) stocking densities affect current herbage yield. We conclude that, while desertification has taken place, grazing over the last decade has not been the cause of this reduced productivity. DOI:10.2458/azu_jrm_v53i2_ward

Are Namibia's grasslands desertifying?

We compared the herbage standing crop on 31 farms along a rainfall gradient in Namibia (southwestern Africa) in 1997 with the results attained for the same gradient by Walter (1939). We found that the slope for the regression of herbage yield on mean annual rainfall in 1997 was 5.93, i.e. 5.93 kg herbage was produced per hectare for every 1 mm increase in rainfall along the gradient. This regression slope is considerably lower than that in Walter's (1939) study (slope = 10.34). Thus, current grassland productivity per unit of rainfall in Namibia is about half that of 50 years ago. There is no evidence of a change in annual rainfall over this period, nor is there any evidence that either short-term (current) or longer-term (11 years) stocking densities affect current herbage yield. We conclude that, while desertification has taken place, grazing over the last decade has not been the cause of this reduced productivity.

Invariance of the design storm in a region under a rainfall climate change at mid-latitudes

The effect of climate change on severe storms is a topic of interest for water resources engineering and hydrometeorology. The question that arises is whether a climate change that increases the local rainfall, also implies an increase in severe storms intensity. In this paper the question is answered using statistical techniques with reference to a type of severe storm: The one that, each year, produces the annual maximum of daily rainfall. Time series of annual maximum of daily rainfall are used to calculate the design storm. The design storm is used in water resources for designing some types of hydraulic structures for flood control, or urban stormwater drainage. This research analyzes whether a climate change in the annual rainfall implies a climate change in the annual maximum of daily rainfall. Evidence is presented showing that these two types of time series have uncoupled evolution. The region of study is semi-arid, located in mid-latitudes, in central Argentina. A climate change in annual rainfall is detected at two sites. Annual rainfall has been increasing at a mean trend of 8 mm/year. However, the annual maximum of daily rainfall has shown a constant mean, at a 5% level of significance. The variance of the annual maximum of daily rainfall has remained constant. This result indicates that the design storm is invariant in a region of central Argentina where a strong climate change in annual rainfall is taking place. It also indicates that a rainfall climate change in a time scale, does not necessarily imply the existence of a similar climate change in embedded time scales.

Response of eolian geomorphic systems to minor climate change: examples from the southern Californian deserts

Eolian processes and landforms are sensitive to changes in atmospheric parameters and surface conditions that affect sediment supply and mobility. The response of eolian geomorphic systems to minor climate change can be examined through process-response models based on a combination of relations between short-term changes in climatic variables and eolian activity and the geologic and geomorphic record of Holocene eolian activity. At both time scales, eolian activity in southern Californian deserts is strongly controlled by variations in precipitation. Wind energy is not a limiting factor in this region. Formation of eolian deposits is a product of climatic changes that increase sediment supply from fluvial and lacustrine sources and may, therefore, be closely tied to periods of channel cutting and geomorphic instability. During intervening periods, eolian deposits migrate away from sediment source areas and are reworked, modified, and degraded. Remobilization of existing dormant dunes is a product of reduced vegetation cover and soil moisture in periods of drier climates. The major control on these processes is decadal to annual changes in rainfall that determine vegetation cover and soil moisture content.

Rainfall and the population dynamics of elephant dung‐piles in the forests of southern Ghana

Decaying dung‐piles were observed at three sites in the lowland forests of southern Ghana. Time to disappearance was inversely related to rainfall in the month of deposition. The monthly survival of each age‐class decreased with age and was inversely proportional to rainfall in the month of deposition. A simulation revealed that if elephant numbers and defaecation rates are constant, then dung density in a given month will be governed by rainfall in the two preceding months. Changes in annual rainfall and its monthly distribution in southern Ghana mean that dung‐pile densities will vary from one month to the next, and between the same months in different years, even if elephant numbers are constant. Thus dung counters must take rainfall into account. A new method of censusing elephants in Ghana is presented, and suggestions are made for improving elephant counts in central African forests.