Climate, Volume 1, Issue 3 (December 2013) – 4 articles , Pages 84-167

Climate change captured my interest as a teenager when, at the dining table, my dad talked about potential anthropogenic climate changes. He brought up subjects such as “climate could change if the Siberian Rivers were to be deviated to the South for irrigation of the (semi) arid areas of the former Soviet Union”. Other subjects were afforestation in the Sahel to enhance precipitation recycling, deforestation in the Tropics that could have worldwide impacts on climate, the local climate impacts of the Merowe High Dam in its vicinity and downstream, Atlantropa, a new ice age, and the increase in days with sunshine after the introduction of the high-chimney policy in the Rhein-Ruhr area, just to mention a few. [...] Full article

In the wake of increasing flood disasters, there is an increasing use of flood inundation models to assess risks and impacts at different temporal and spatial scales. Assessing the impacts of extreme climatic rainfall events will require developing design rainfall profiles to represent rainfall under different conditions. Rainfall profiles of different return periods were developed using the Flood Estimation Handbook (FEH) methodology for a small rural catchment of Scotland, to assess flood risks at a catchment scale. Rainfall induced runoff flows were estimated based on a set of catchment characteristics. The channel and floodplain flows were modelled using a two-dimensional hydrodynamic model-TUFLOW. The main channel was represented by a one-dimensional linear channel based on surveyed data and the floodplain topography, was represented by a digital terrain model based on Light Detection and Ranging (LiDAR). A range of hydrological events with different return periods are simulated. Results show that many residential houses and an extensive area of agricultural land are at risk of flooding from extreme events such as a 1 in 100 year flood. Full article

The majority of studies assessing aerosol effects on rainfall use coarse spatial scale (1° latitude/longitude or more) and multi-seasonal or decadal data sets. Here, we present results from a spatial correlation of aerosol size distribution and rain rate for selected stratiform and cumuliform precipitation events. The chemistry transport version of the Weather Research and Forecasting model was used to estimate aerosol parameters during rain events Aerosol maps were then compared with observations of rainfall using geostatistics for the first time. The cross-variogram analysis showed that anthropogenic aerosol was associated with areas of less intense rain within the stratiform system studied. For cumuliform systems, cross-variogram analysis found that anthropogenic emissions may be associated with enhanced rain downwind of aerosol emissions. We conclude that geostatistics provides a promising new technique to investigate relationships between aerosols and rainfall at spatial scales of 1 km which complements more commonly used methods to study aerosol effects on rainfall. Full article

Seasonal and inter-annual variabilities in aerosol optical depth (AOD) andaerosol size distribution are investigated using ground-based measurements (sun photometersand sun/sky radiometers), and MODIS (MODerate Imaging Spectroradiometer) and MISR(Multiangle Imaging SpectroRadiometer) satellites over Ahmedabad, Gurushikhar, Karachi,Kanpur and Gandhi College in South Asia during 2006–2008. An analysis and a review onthe comparison between aerosol optical depths measured from ground-based observationsand remote sensing over South Asia is performed. Karachi and Ahmedabad AODs aretwo times higher than Gurushikhar, a high altitude remote site. AODs over Kanpur andGandhi College in the Indo-Gangetic basin are higher than those measured over Ahmedabad,Gurushikhar and Karachi. Summer monsoon AODs are higher over Ahmedabad andKarachi, while winter AODs are higher over Kanpur and Gandhi College. AOD ratio,ratio of AODs obtained at 0.38 μm and 0.87 μm, is higher during postmonsoon andwinter than premonsoon and monsoon ratio suggesting the abundance of fine mode aerosolsduring postmonsoon and winter. Monsoon AOD ratios are lowest owing to the dominanceof coarse mode (mainly sea salt) particles. Ångström wavelength exponent (α) duringpostmonsoon and winter are higher than that of premonsoon and monsoon values. Lower α values over Gurushikhar and Karachi indicate the dominance of coarse mode aerosols(dust in Gurushikhar, and dust and sea salt in Karachi). Dominance of fine mode aerosolsdue to anthropogenic activities give rise to higher α values over urban locations (e.g.,Ahmedabad and Kanpur). Comparison between ground-based and MODIS (Terra andAqua) retrieved AODs show that aerosol optical depths do not change significantly inan hour and much of the diurnal AOD variation is captured well by the two MODISinstruments. The temporal difference (about an hour) between the ground-based and remotesensing measurements contributes negligibly to the observed differences in AODs. Thedifferences between ground-based and remote sensing (MODIS and MISR) AODs vary onspatial scales. During the study period (2006–2008) MODIS underestimates AODs overwestern India by about 0.04, while over the Indo-Gangetic Plain MODIS overestimatesAOD by 0.06 in (Kanpur) and underestimates by 0.07 (Gandhi College) with respect toAODs measured by hand held sun photometer and Microtops sun photometer (Ahmedabadand Gurushikhar), and AERONET sun/sky radiometers (Karachi, Kanpur and GandhiCollege) respectively. During the same period MISR underestimates AODs in the rangeof 0.02–0.17 over Ahmedabad, Gurushikhar, Karachi and Kanpur, while in Gandhi CollegeMISR overestimates AOD by 0.2 when compared to ground-based AODs. Results on spatial,seasonal and inter-annual variations in aerosol characteristics will be useful in improving theaerosol retrieval algorithms in remote sensing, and in regional and global estimates of aerosolradiative forcing. Full article