Drought Occurrence Probability Analysis Using Multivariate Standardized Drought Index and Copula Function Under Climate Change

This study aims to investigate the effect of climate change on the probability of drought occurrence in central Iran. To this end, a new drought index called Multivariate Standardized Drought Index (MSDI) was developed, which is composed of the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Soil Moisture Index (SSI). The required data included precipitation, temperature (from CRU TS), and soil moisture (from the ESA CCA SM product) on a monthly time scale for the 1980–2016 period. Moreover, future climate data were downloaded from CMIP6 models under the latest SSPs-RCPs emission scenarios (SSP1-2.6 and SSP5-8.5) for the 2020–2056 period. Based on the normalized root mean square error (NRMSE), Cramer-von mises statistic (S_n), and Nash Sutcliffe (NS) evaluation criteria, the Galambos and Clayton functions were selected to derive copula-based joint distribution functions in both periods. The results showed that more severe and longer droughts will occur in the future compared to the historical period and in particular under the SSP5-8.5 scenario. From the derived joint return period, a drought event with defined severity or duration will happen in a shorter return period as compared with the historical period. In other words, the joint return period indicated a higher probability of drought occurrence in the future period. Moreover, the joint return period analysis revealed that the return period of mild droughts will remain the same, while it will decrease for extreme droughts in the future.

     

Water Management of Irrigation Dams Considering Climate Variation: Case Study of Zayandeh-rud Reservoir, Iran

Dependency of reservoir operation on the climate variation occurs especially in regions, where agricultural demand has a significant share of the total water demands. The variability between demands that are based on annual climate conditions may be larger than the uncertainty associated with other explanatory variables in long-term operation of an irrigation dam. This paper proposed a rule curves to the water managers of the Zayandeh-rud reservoir in Iran in long-lead reservoir operation. A regional optimal allocation of water among different crops and irrigation units is developed. The optimal allocation model is coupled with a reservoir operating model, which is developed based on the certain hedging that deals with the available water and the water demands mutually. This coupled model is able to activate restrictions on allocating water to agricultural demands considering variation of inflow to the reservoir, variation of demands and the economic value of allocating water among different crops and irrigation units. The resulted rule curve is presented with a number of tables for more details and accuracy and a simple curve, which is more useful for operational purpose.     

CoFe2O4@methyl cellulose core-shell nanostructure and their hybrids with functionalized graphene aerogel for high performance asymmetric supercapacitor

Recently, the use of asymmetric supercapacitors (ASC) has attracted much attention due to their optimum storage of energy and a high range of voltage. Here, we have indicated the design and fabrication of a unique ASC based on metal-spinel core-shell nanocomposite (CoFe₂O₄@MC) as a positive electrode and a p-phenylenediamine (PPDA)-graphene aerogel composite (AP) as a negative electrode in aqueous KOH electrolyte solution. The CoFe₂O₄@MC nanocomposite was prepared by the chemical deposition method. The AP was also effortlessly organized using the hydrothermal method. Considering the incorporation of methylcellulose carbohydrate polymer (MC) into the CoFe₂O₄ nanomaterial and consequently having a porous structure, a specific capacitance of 433.3 F g^?1 was obtained at the current density of 1 A g^?1 with the configuration of three electrodes. The CoFe₂O₄@MC//AP-ASC operates in the voltage range up to 2.3 V and provides a specific capacitance of 99 in 1 A g^?1. It presents an impressive energy density and power density of ~73 W h Kg^?1 and 1056 W kg^?1, respectively which prove its quality. The most important feature seems to be good cycling stability and capacity retention of 89% after 2000 cycles. These splendid outcomes show that CoFe₂O₄@MC nanocomposite possibly seems to be a satisfying choice for the next generation of devices with the capability of energy storage.