Mapping flood vulnerability using an analytical hierarchy process (AHP) in the Metropolis of Mumbai.

The burgeoning significance of urban floods in the context of evolving climate dynamics and shifting rainfall patterns underscores the exigency for comprehensive investigation and mitigation strategies. The study employs a multi-criteria assessment (MCE) approach and the analytical hierarchy process (AHP) to evaluate flood-vulnerable zones, wards, and sub-category-wise flood locations in Greater Mumbai. The AHP technique is used to evaluate flood-vulnerable impacting parameters such as rainfall (29.42%), slope (20.96%), land use/land cover (17.52%), vicinity to sewers and storm-water drainage (13.99%), vicinity to natural drainage (8.97%), vegetation (5.58%), and soil (3.56%). The study area is classified under different vulnerable categories as severe vulnerable (46.72%), high to very high (18.74%), and slight to moderate (34.54%). Researchers analysed 234 waterlogged locations, revealing that 85.46% (200 locations) were in the severe to very high vulnerability category, and only 14.52% (34 locations) were in the other three categories. Flood locations are more affected by slope (under the categories of < 5 m and 5.01-10 m), built-up land, sewers and storm water drainage (< 125 m), natural drainage (< 250 m), rainfall (< 2000 to 2200 mm), lowest dense vegetation, and coastal alluvium in soils. These model-based flood vulnerability maps are crucial for planning flood conservation and mitigation measures.

Paradoxical behaviour of rainfall and temperature over ecologically sensitive areas along the Western Ghats.

Initial reports signify some specific isolated locations in different latitudes, revealing a paradoxical increase in both heavy and very heavy rainfall events and also an increment in total, i.e., in both rainfall and temperature, over ecologically sensitive areas along the Western Ghats (WG). This paper presents a coherent study of the full-scale of daily rainfall and temperature over 27 well-spaced stations in the study area to determine its extent and investigate whether or not this contradictory behaviour is real. Also, an attempt has been made to assess the differential behaviour of rainfall, temperature, and heavy rainfall events in association with land use and land cover change (LULC). The analysis revealed that rainfall and temperature over the study area are increasing, whereas heavy rainfall events have increased during 1981-2020 with strong peaks after 2000 around 18-19°N (Mumbai metropolitan region), 14-16°N (mining and quarrying regions in Goa), and 9-12°N (a narrow strip of land spanning across the coastal towns of Karnataka and Kerala) latitudes. The majority of the rainfall excess years coincided with El Nino years, indicating that El Nino does not affect rainfall negatively. However, rainfall over the WG is influenced by local relief and cascading topography. The spatial pattern of average annual rainfall shows a decreasing trend from south to north because the elevation and span of rainfall occurrence are higher in the southern part of WG. The findings of the current research will help in building a strategy to address trends and patterns of climatic variables in association with LULC.

Role of Seawater Ions in Forming an Effective Interface between Photocatalyst/Cocatalyst.

Photocatalytic (PC) hydrogen production from water splitting is a promising route to fulfill the current energy demand in a sustainable manner. For photocatalysis to become industrially viable, seawater should be used as an ideal solvent. Until now, a variety of semiconductor photocatalysts have been exploited for seawater splitting; however, there has been a lack of a well-established catalytic system for seawater splitting, as seawater ions have an uncertain effect on water splitting. Recently, ionized carbon nitride PC has been shown to substantially enhance water splitting in the presence of ions; however, the underlying manner by which the ions promote PC has still not been fully understood. Presented here is a systematic evaluation of an ionized low-cost carbon nitride-based semiconductor for seawater splitting. A detailed study has been done using this salt-type semiconductor in the presence of a variety of ions (Na+, K+, Mg2+, Ca2+, Cl-, SO42-), and their role has been probed in modulating the photocatalytic activity. Multiple measurements have provided insight as to how the presence of cations aid advantageously in forming an effective in situ interface between catalyst/cocatalyst for improved electron transfer. Previously, these ions were purported to change the hole quenching ability only of the photocatalyst, whereas here it has been shown that the change in the electron transfer ability of the photocatalyst to cocatalyst appears to be the cause for augmented PC. This improved interfacial electron transfer has been used to rationalize the 8-fold enhancement in the photocatalytic rate in the presence of simulated seawater compared to deionized water and provides the impetus for the use of ionized carbon nitride structures for sustainable PC splitting of seawater.