Mesoscale Climate Model Research Articles

Quantification of land use/land cover changes in Pearl River Delta and its impact on regional climate in summer using numerical modeling

This study quantified land use/land cover (LULC) changes in Pearl River Delta (PRD) of South China and its impact on regional climate over the last two decades. The LULC change analyses were accomplished by applying a change detection method to a set of Landsat imagery and ancillary data acquired from 1970s to 2000. The results indicate that the urban expansion is the prevailing LULC change in the PRD. Impact of LULC change on regional climate was simulated by using a mesoscale climate model. Two different land cover datasets circa 1990 and 2000 were input to the model to investigate the impact of urbanization on regional weather and climate condition in summer 2005. The simulation results show that rapid urban expansion can substantially alter regional climate conditions in the PRD region including monthly mean temperature, precipitation, moisture, and surface heat fluxes.

Simulation of Landcover Change Influences for Water Availability Using a Regional Atmospheric Model

A study of the landcover change impact on water budget has been done using a mesoscale climate model. A prestine lake catchment of Lake Poso in Central Sulawesi Province has been used for this study. A scenario for deforestation that change forest into savannah was performed for the dry period from July to December 2005 to simulate the severest possible scenario. The results show increase risks of flood during wet season and risks of drought during the dry season with highest increase of surface runoff up to 18% and decrease up to 10%. Meanwhile, the underground runoff increase during wet season up to 17% and decrease up to 10% during the dry season. This study may suitable for the climate change impact study and to simulate the land degradation due to ever increasing deforestation and land clearing.

Examination of the Bouchet–Morton Complementary Relationship Using a Mesoscale Climate Model and Observations under a Progressive Irrigation Scenario

AbstractThe complementary relationship between actual and potential evaporation over southeastern Turkey was examined using a mesoscale climate model and field data. Model simulations of both actual and potential evaporation produce realistic temporal patterns in comparison to those estimated from field data; as evaporation from the surface increases with increasing irrigation, potential evaporation decreases. This is in accordance with the Bouchet–Morton complementary relationship and suggests that actual evapotranspiration can be readily computed from routine meteorological observations. The driving mechanisms behind irrigation-related changes in actual and potential evaporation include reduced wind velocities, increased atmospheric stability, and depressed humidity deficits. The relative role of each in preserving the complementary relation is assessed by fitting a potential evaporation model to pan evaporation data. The importance of reduced wind velocity in maintaining complementarity was unexpected, and thus examined further using a set of perturbation simulation experiments with changing roughness parameters (reflecting growing cotton crops), changing moisture conditions (reflecting irrigation), and both. Three potential causes of wind velocity reduction associated with irrigation may be increased surface roughness, decreased thermal convection that influences momentum transfer, and the development of anomalous high pressure that counteracts the background wind field. All three are evident in the mesoscale model results, but the primary cause is the pressure-induced local wind system. The apparent necessity of capturing mesoscale dynamical feedbacks in maintaining complementarity between potential and actual evaporation suggests that a theory more complicated than current descriptions (which are based on feedbacks between actual evaporation and temperature and/or humidity gradients) is required to explain the complementary relationship.

MODIS-Derived Boundary Conditions for a Mesoscale Climate Model: Application to Irrigated Agriculture in the Euphrates Basin

AbstractIn arid and semiarid parts of the world, evaporation from irrigated fields may significantly influence humidity, near-surface winds, and precipitation. Using Moderate Resolution Imaging Spectroradiometer (MODIS) Terra imagery from summer and autumn 2000 the authors attempt to improve the realism of a regional climate model (the fifth-generation Pennsylvania State University–NCAR Mesoscale Model) with respect to irrigated agriculture. MODIS data were used to estimate spatially distributed vegetation fraction and to identify areas of irrigated land use. Additionally, a novel surface flux routine designed to simulate traditional flood irrigation was implemented. Together these modifications significantly improved model predictions of water flux and the surface energy balance when judged against independent weather station data and known crop requirements. Model estimates of watershed-level water consumption were more than doubled relative to simulations that did not incorporate MODIS data, and there were small but systematic differences in predicted temperature and humidity near the surface. The modified version of the mesoscale model also predicts the existence of heat-driven circulations around large irrigated features, and these circulations are similar in structure and magnitude to those predicted by linear theory. Based on these results, it was found that accurate representation of irrigated agriculture is a prerequisite to any study of the impact of land-use change on climate or on water resources.

東京２３区における公園緑地のヒートアイランド現象緩和効果

The purpose of this study is to investigate how to solve the urban heat island problem in central Tokyo by appropriate greenerization. To estimate the effect of the existing green spaces and proposed greening plans on the urban heat island in Tokyo area(30km×36km), the distributions of air temperature at 14:00 and 21:00 on typical summer day of eleven cases were calculated by using a numerical simulation with a mesoscale climate model. Then, the cost-effectiveness of two typical cases was calculated. The following results were obtained, 1) The air temperature increases at maximum 0.66°C at 14:00 in the western part of Tokyo by green open spaces(56km2) are lost in the areas not protected by city planning designation. This damage is estimated to be 1.8 billion yen per year. 2) Forestation of green spaces protected by city planning designation is the most effective method to cool down the air temperature of large areas. 3) Increasing the ratio of green areas in the central 3 wards is the most effective method to lower the air temperature. 4) Preserving existing green open spaces is important because they do not only absorb CO2, but also prevent discharging CO2 1.45 times bigger than the CO2 they absorb.

Time Series Analysis of 20 Years of Hourly Precipitation in Southwest Michigan

Hourly precipitation data from Oshtemo Township, Michigan, located approximately 55 km east of the lee shore of Lake Michigan, for the period of April 1980 through March 2000 were examined. Diurnal analysis of precipitation as well as time series analysis of precipitation were performed on the study period. An overall nocturnal maximum in the mean accumulation of precipitation was detected during the 2-hour periods before 2000 LST and 2200 LST. Elevated spring and fall accumulations were responsible for this evening maximum. Elevated summer and winter accumulations were responsible for a weak secondary morning maximum. An overall morning maximum in the mean precipitation hours was detected during the 2-hour period before 1000 LST. ARIMA modeling verified that both precipitation accumulations and counts, for all times of the day, were significant at the 5% level. A storm event model was developed from the time series, the resulting values of which can be used as input in mesoscale climate, hydrological, and agricultural computer models: the mean pulse duration was 2.44 hours; the mean interlude between pulses was 37.64 hours; the mean event accumulation was 4.1 mm; and the mean rate was 1.8 mm / hr. Finally, inter-annual analysis performed for the period of 1981 to 1999 showed that there was no statistically significant change in precipitation over the period.

Comparison of climate model results with European vegetation and permafrost during oxygen isotope stage three

Oxygen isotope stage 3 (OIS3), an interstade between approximately 60,000 and 25,000 yr B.P., presents an ideal opportunity to compare high-resolution climate simulations with the geologic record. To facilitate this comparison, the results of a mesoscale climate model (RegCM2) embedded in the GENESIS GCM are utilized to drive a vegetation model (BIOME 3.5). The BIOME output is then compared with OIS3 compilations derived from pollen. The simulated biomes agree well with the pollen-based biomes in southern Europe; however, disagreements occur in the northern part of the domain. The most striking mismatch involves the distribution of tundra. The models fail to have tundra extend to its observed position as far south as 50°N in central Europe during OIS3. The model also fails to have permafrost extend southward to its observed position between 50°N and 55°N in western Europe during OIS3. A variety of sensitivity experiments are performed to investigate these mismatches. These experiments demonstrate the importance of annual and summer temperatures and the length of the winter season in creating improved matches between the model results and the inferred distributions of vegetation and permafrost in northern Europe.

Development and application of a mesoscale climate model for the tropics: Influence of sea surface temperature anomalies on the West African monsoon

A mesoscale climate model (MCM) is developed from the Pennsylvania State University/National Center for Atmospheric Research mesoscale model 5 to simulate the West African summer monsoon. Results from the MCM are compared to observations, a reanalysis, and global climate model (GCM) output to show that the MCM reasonably simulates the West African monsoon climate and its variability and improves on many shortcomings of the GCM simulations. The MCM's ability to capture correctly processes that cause interannual variability, and thereby allow us to improve our physical understanding of that variability, is investigated by examining the influence of Gulf of Guinea sea surface temperature anomalies (SSTAs) on the West African monsoon. Similar to observations, precipitation decreases over the Sahel and increases along the Guinean coast in response to warm SSTAs in the gulf. The increase in rainfall along the Guinean coast is associated with an increase in lower tropospheric water vapor content due to enhanced evaporation over the warm SSTAs and northward moisture advection in the monsoon flow. This stronger precipitation on the coast occurs despite a decrease in the land/sea temperature gradient, which is the fundamental driver of the monsoon. The decrease in rainfall over the southern Sahel is associated with lower tropospheric subsidence replacing rising vertical motions as the monsoon circulation is shifted equatorward. Dynamically, the subsidence over the southern Sahel is associated with shrinking of both planetary and relative vorticity. The former is related to the equatorward shift of the monsoon, which results in an expansion of the equatorward flow from the Sahel to the northern Guinean coast. The latter occurs because the equatorward flow over the southern Sahel occurs lower in the troposphere (i.e., 850 mbar) than in the control (i.e., 700 mbar), where the meridional relative vorticity gradient is opposite to the gradient at 700 mbar.

Thermal environment simulation for three dimensional replacement of urban activity

Abstract The effect of a three-dimensional replacement of urban thermal environment activity is discussed on the basis of numerical simulation with a mesoscale climate model. Given a three-dimensional replacement of urban activity, greater concentration decreased surface air temperatures. Such concentration is apparently effective for modifying the thermal environment during the daytime, while the reduction of energy consumption is more effective during the night-time. Through sensitivity analysis, it is shown that building width and height variations with associated drag effects modify the environment near the ground.

Evidence that local land use practices influence regional climate, vegetation, and stream flow patterns in adjacent natural areas

AbstractWe present evidence that land use practices in the plains of Colorado influence regional climate and vegetation in adjacent natural areas in the Rocky Mountains in predictable ways. Mesoscale climate model simulations using the Colorado State University Regional Atmospheric Modelling System (RAMS) projected that modifications to natural vegetation in the plains, primarily due to agriculture and urbanization, could produce lower summer temperatures in the mountains. We corroborate the RAMS simulations with three independent sets of data: (i) climate records from 16 weather stations, which showed significant trends of decreasing July temperatures in recent decades; (ii) the distribution of seedlings of five dominant conifer species in Rocky Mountain National Park, Colorado, which suggested that cooler, wetter conditions occurred over roughly the same time period; and (iii) increased stream flow, normalized for changes in precipitation, during the summer months in four river basins, which also indicates cooler summer temperatures and lower transpiration at landscape scales. Combined, the mesoscale atmospheric/land‐surface model, short‐term trends in regional temperatures, forest distribution changes, and hydrology data indicate that the effects of land use practices on regional climate may overshadow larger‐scale temperature changes commonly associated with observed increases in CO2 and other greenhouse gases.

Evidence that local land use practices influence regional climate, vegetation, and stream flow patterns in adjacent natural areas

We present evidence that land use practices in the plains of Colorado influence regional climate and vegetation in adjacent natural areas in the Rocky Mountains in predictable ways. Mesoscale climate model simulations using the Colorado State University Regional Atmospheric Modelling System (RAMS) projected that modifications to natural vegetation in the plains, primarily due to agriculture and urbanization, could produce lower summer temperatures in the mountains. We corroborate the RAMS simulations with three independent sets of data: (i) climate records from 16 weather stations, which showed significant trends of decreasing July temperatures in recent decades; (ii) the distribution of seedlings of five dominant conifer species in Rocky Mountain National Park, Colorado, which suggested that cooler, wetter conditions occurred over roughly the same time period; and (iii) increased stream flow, normalized for changes in precipitation, during the summer months in four river basins, which also indicates cooler summer temperatures and lower transpiration at landscape scales. Combined, the mesoscale atmospheric/land-surface model, short-term trends in regional temperatures, forest distribution changes, and hydrology data indicate that the effects of land use practices on regional climate may overshadow larger-scale temperature changes commonly associated with observed increases in CO2 and other greenhouse gases.

Sensitivity of regional climate to deforestation in the Amazon basin

Deforestation results in several adverse effects on the natural environment. The focus of this paper is on the effects of deforestation on land-surface processes and regional climate of the Amazon basin. In general, the effects of deforestation on climate are likely to depend on the scale of the deforested area. In this study, we are interested in the effects due to deforestation of areas with a scale of about 250 km. Hence, a meso-scale climate model is used in performing numerical experiments on the sensitivity of regional climate to deforestation of areas with that size. It is found that deforestation results in less net surface radiation, less evaporation, less rainfall, and warmer surface temperature. The magnitude of the change in temperature is of the order of 0·5°C, the magnitudes of the changes in the other variables are of the order of 10%. In order to verify some of the results of the numerical experiments, the model simulations of net surface radiation are compared to recent observations of net radiation over cleared and undisturbed forest in the Amazon. The results of the model and the observations agree in the following conclusion: the difference in net surface radiation between cleared and undisturbed forest is, almost, equally partitioned between net solar radiation and net long-wave radiation. This finding contributes to our understanding of the basic physics in the deforestation problem.