ABSTRACT
Results of a detailed computation of trends in the annual and the seasonal extreme climate indices using the observed daily temperature and precipitation datasets from a total of 19 stations ...from Saudi Arabia (SA) for the 30‐year period (1979–2008) are presented. The temperature based indices have higher value of statistically significant decadal trends and are spatially more widespread as compared to the precipitation based indices. The increase in the frequency of the extreme warm temperatures is larger than the increase in the frequency of the extreme cold temperatures, both on the annual and the seasonal basis. The daily temperature based extremes display more warming in the summer season. The (southwest) coastal stations have displayed more warming as compared to the inland stations. The regional daily temperature range shows a statistically significant increase of 0.21 °C decade−1 for SA, during the 30‐year period. Warming of extreme maximum temperatures follow the general trend of already noticed warming in SA.
Salinity is a widespread soil problem limiting productivity of oilseed crops worldwide. Reduction in growth generally associated with decline in photosynthesis. Accumulation of osmo‐protectants such ...as glycinebetaine (GB) permits the plant to cope with salt stress. This study was aimed to understand the mechanism by which exogenous GB application improves photosynthetic capacity and salt tolerance in two diverse lines of canola differing in salt tolerance using chlorophyll fluorescence technique. Glycinebetaine was applied as foliarly or through rooting medium to two canola lines Dunkeld and Cyclone that were grown under non‐saline or saline conditions. Root‐applied GB caused adverse effects whereas foliar application of GB was effective in improving growth of canola cultivars. However, the response of salt‐tolerant cultivar Dunkeld was stronger than that of salt sensitive Cyclone. Foliar application of GB improved accumulation of proline and plant water status. Application of GB enhanced the photosynthetic CO2 fixation, stomatal conductance (gs) and water‐use efficiency. The tolerant lines Dunkeld had more responsive to GB application. Chlorophyll fluorescence measurements (Fo, Fm, Fv, Fo/Fm, Fv/Fo and Fv/Fm ratios) revealed that salt stress reduced energy trapping efficiency by damaging oxygen evolving complex, over reduction of QA resulting in occurrence of chronic photoinhibition. However, exogenous GB protected the oxygen evolving centre of PSII and maintains activity of PSII. Although root‐applied GB adversely affected the growth of canola plants, it did not have any adverse effect on PSII photochemistry. Moreover, fluorescence parameters could provide a rapid means for determining salt tolerance in canola and could be a rapid and sensitive test to identify genotypes highly tolerant to salt stress.
The precipitation variability, trends, and teleconnections are studied over six administrative regions of Pakistan (Gilgit-Baltistan or GB, Azad Jammu and Kashmir or AJK, Khyber Pakhtoonkhawa or KPK, ...Punjab, Sindh, and Balochistan) on multiple timescales for the period of recent 38 years (1976–2013) using precipitation data of 42 stations and circulation indices datasets (Indian Ocean Dipole IOD, North Atlantic Oscillation NAO, Arctic Oscillation AO, El Niño Southern Oscillation ENSO, Pacific Decadal Oscillation PDO, Atlantic Multidecadal Oscillation AMO, and Quasi-Biennial Oscillation QBO). The summer monsoon season received the highest precipitation, amounting to 45%, whereas the winter and pre-monsoon (post-monsoon) seasons contributed 30 and 20% (5%), respectively, of the annual total precipitation. Positive percentile changes were observed in GB, KPK, Punjab, and Balochistan regions during pre-monsoon season and in Balochistan region during post-monsoon season in second half as compared to first half of 38-year period. The Mann-Kendall test revealed increasing trends for the period of 1995–2013 as compared to period of 1976–1994 for entire Pakistan during monsoon season and on annual timescale. A significant influence of ENSO was observed in all the four seasons in Balochistan, KPK, Punjab, and AJK regions during monsoon and post-monsoon seasons. This study not only offers an understanding of precipitation variability linkages with large-scale circulations and trends, but also it contributes as a resource document for policy makers to take measures for adaptation and mitigation of climate change and its impacts with special focus on precipitation over different administrative regions of Pakistan.
The analyses of monthly and annual variability, and the seasonal teleconnections with the Indian Ocean Dipole (IOD), El‐Niño Southern Oscillation (ENSO), and the North Atlantic Oscillation (NAO) ...circulation indices, for rainfall from 26 stations in Saudi Arabia (SA), for 33‐year period (1978–2010), are presented. High interannual variability with non‐monsoonal annual cycle characterizes the rainfall climate of SA in recent 33‐year period. Eight of 26 stations display statistically significant simultaneous teleconnections with IOD and ENSO in the September–October–November (SON) season. These eight stations are situated north of 21.50°N (nSA) and are located in northern and in southeastern regions of nSA.
The interseasonal variability of two basic climatic parameters (precipitation and temperature) is assessed, over vulnerable and data sparse region of Pakistan (23° to 37°N and 60° to 75°E), for two ...Coupled Model Intercomparison Project 3 (CMIP3) based Atmospheric-Oceanic General Circulation Model (AOGCM) versions: CM2.0 and CM2.1 by Geophysical Fluid Dynamics Laboratory (GFDL), and two CMIP5 based AOGCM versions: CM2p1 and CM3.0. A recent historical 50-year period (1951–2000) is analyzed and compared with APHRODITE for precipitation and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis based gridded datasets for temperature for the following four seasons: DJF, MAM, JJA, and SON. The study area is divided into three regions: all Pakistan, northern Pakistan, and southern Pakistan. The interseasonal variability of the precipitation and the temperature are derived from all three (five) runs of CM2.0 (CM2.1) and from all ten (five) runs of CM 2p1 (CM3.0). The bias, root mean square error (RMSE), one-sigma standard deviation (SD) and correlation coefficient (CC) are used as assessing metrics. The following individual runs have positive CC with respect to APHRODITE at ≤1% Confidence Level (CL). On seasonal basis for CMIP5 based GFDL models during DJF: CM2p1R5 (for all Pakistan), CM2p1R5 (for northern Pakistan), and during MAM: CM2p1R5 (for southern Pakistan; this run has the lowest centered RMSE of 0.11 mm/day), whereas on annual basis: CM3.0R3 (for all Pakistan). However, out of these four runs, only CM2p1 (for southern Pakistan) has SD < SD
obs
(0.08 < 0.12 mm/day). There are 13 other runs for which the positive CC is at ≤5% CL, both relative to observed precipitation or temperature. Out of these 13 runs, only the average of runs of GFDL-CM2.1 in CMIP3 in JJA in southern Pakistan has SD < SD
obs
(0.56 < 0.59 °C) with a centered RMSE value of 0.65 °C. These characteristics of GFDL-CM2p1 runs are supported by their relatively better simulation of spatial distribution of 1000–850 hPa averaged layer wind patterns, relative to NCEP/NCAR 1000–850 hPa averaged wind patterns, over Pakistan, in respective seasons. A variance based bias adjustment when applied displays considerable interseasonal bias reduction both in precipitation and temperature in long term mean with no change in trend.
Soil salinity is a major environmental constraint to crop productivity worldwide. The “biological” approach to this problem focuses on the management, exploitation, or development of plants able to ...thrive on salt‐affected soils. This chapter reviews strategies by which plants can be enabled to grow on saline soils. The first strategy is to prime seeds before planting by treating them with inorganic or organic chemicals and/or with high or low temperatures. The second strategy involves exogenous application of organic chemicals, such as glycine betaine, proline, or plant growth regulators, or inorganic chemicals to plants under salinity stress. Considerable improvements in growth and yield have been reported in a number of crops using these approaches. The third strategy is to employ selection and breeding. Major efforts have been made to develop salt‐tolerant lines or cultivars of crops using conventional plant breeding. However, the complexity of the tolerance mechanisms, lack of selection criteria, and variation in responses of plants at different developmental stages have resulted in only limited success. The emphases for developing salt‐tolerant lines/cultivars are now on marker‐assisted breeding and genetic transformation. The development of salt‐tolerant transgenic plants is still at an early stage but may become increasingly more effective as better knowledge of the complex mechanisms involved in plant salt tolerance is acquired. Furthermore, the rapid expansion in knowledge on genomics and proteomics will undoubtedly accelerate the transgenic and molecular breeding approaches However, to date, there are few conclusive reports indicating successful performance of transgenic cultivars under natural stressful environments.
ABSTRACT
Wet (dry) spells can cause extreme climatic conditions, such as floods (droughts) which can adversely influence the natural resources. A spatio‐temporal analysis of observed wet and dry ...spells is carried out for vulnerable and data sparse region of Pakistan (24°–38°N and 61°–78°E). Observed monthly precipitation data sets from 46 weather station are used for a length of consecutive 32 years (1976−2007). Additionally, after bias adjustment, the Asian Precipitation Highly‐Resolved Observational Data Integration Towards Evaluation (APHRODITE) precipitation data set, abbreviated as APH, is utilized to corroborate the findings. For both data sets, a threshold of 1 mm is used to define a wet spell. Decadal variability of precipitation for observed and APH data sets indicates that there is gradual decrease in wet spell length for arid and humid regimes, as compared to semi‐arid regimes where there is no change in wet spell length. Monthly dry and wet slope difference (SD), on a log–log plot between number of spells and spell length, is used to classify precipitation regimes in Pakistan, for the first time. A weather station is categorized as humid if SD is less than −2.38 in units of number of spells per length of spells. If SD lies between −2.37 and −0.51, then the weather station is classified as semi‐arid and if SD is greater than −0.51, then it is classified as arid. Thus, according to SD classification, 66% of area in Pakistan is arid, whereas 30% (4%) is semi‐arid (humid). Comparison of precipitation regimes based upon observed and APH data sets with other climate classification schemes that involve both precipitation and temperature is presented.
Monthly dry and wet slope difference (SD), extracted from log–log plot between number of spells and spell length, is used to classify precipitation regimes in Pakistan, and is displayed in upper row panels using observed and Asian Precipitation Highly‐Resolved Observational Data Integration Towards Evaluation precipitation data sets. The Erniç aridity index and Köppen classification technique‐based results are compared in lower row panels. Weather station locations are displayed using open circles.
Variability in the observed daily temperature for the 31-year period (1978–2008) is studied for northern Saudi Arabia (nSA) by computing the probability distribution functions (PDFs) on a seasonal ...basis. The 31-year base period is divided into three decades and the results for the first (1978–1987) and the last decade (1999–2008) are presented. When averaged over all seasons, mean values of the observed decadal PDFs depict a positive shift from the first to last decade in the minimum, mean, and maximum temperature of 0.81 °C, 1.03 °C, and 1.25 °C, respectively. The daily temperature datasets from a regional climate model (RCM) and two versions of a coupled atmosphere-ocean general circulation model (AOGCM) are compared with the observed daily temperature datasets. The RCM is driven by re-analysis data for the historical period and by the HadCM3 model for the future, while the AOGCMs used are the GFDL CM2.0 and 2.1 models, with both HadCM3 and the GFDL simulations corresponding to the SRES A1B scenario. The average shifts from 1978–1987 to 1999–2008 in the mean value of the PDFs for the minimum, mean and maximum temperature are 0.63 °C, 0.54 °C and 0.45 °C, respectively, for the RCM, and 0.97 °C, 0.97 °C and 0.96 °C, respectively, for the AOGCM. Thus, the RCM shows a smaller shift in the mean of PDF for maximum temperature than for mean or minimum temperature, the AOGCM shows a comparable shift for all three, and the observations show a greater shift in the PDF for maximum temperature. For the period 2070–2099 relative to 1978–2008, the three average shifts are 4.11 °C, 3.87 °C and 3.44 °C for the RCM and 3.63 °C, 3.74 °C and 3.84 °C for the AOGCM.
Spatiotemporal variability in the observed daily temperatures for a recent 30-year period (1986–2015) is examined from a total of 18 different weather stations in the Hindukush, Karakoram and ...Himalaya region in northern Pakistan (HKNP) by employing probability distribution functions (PDFs) on annual and seasonal basis. The region is a hub of glaciers and perennial snow cover which fulfills a large fraction of Pakistan’s water demand for irrigation, power generation and for drinking purposes. The temperature-based PDFs show a significant mean decadal warming of 0.45 °C, 0.03 °C, and 0.25 °C, in the maximum (Tmax), minimum (Tmin) and mean temperature (Tmean) of the region, on annual basis, respectively. However, the observed river discharges-based PDFs of the region show a mean negative decadal shift of − 40.15 m
3
/s on annual basis. The negative decadal shift in river discharge in warm climate is discussed in terms of percentile-based analysis which quantifies temperature changes for each percentile. The results revealed that the decadal changes in Tmin percentiles are more correlated with river discharge than decadal changes in Tmax and Tmean percentiles, on annual basis. The seasonal analysis showed a significant positive decadal shift of 1.93 °C for Tmax in spring season, whereas winter season showed a significant negative decadal shift of − 0.56 °C in Tmin of the HKNP region, from first decade (1986–1995) to third decade (2006–2015), respectively. The rest of seasons (i.e., summer and autumn) displayed high variability in the Tmax, Tmin and Tmean in the HKNP region. A high observed (non-parametric) correlation between the observed cloud cover and temperatures of the region indicates that changes in regional cloud cover may influence the regional temperatures. This work highlights the importance of recent temperature variations in the HKNP and its connection with the downstream river discharge of the region in changing climate of northern Pakistan.
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