Shijo Joseph is taking an account of water-logged lives in Kerala. A scientist working with GIS and satellite data for the Kerala Forest Research Institute (KFRI), his first brief is a ground survey in the Chalakudy river basin. He is looking for the high water mark left on the walls to measure how far water has risen from the ground up. These ground control points help validate satellite-based remote sensing data later. The inundation lines are clearly visible on the walls of the buildings where wetness or remnants of flood such as small particles, floating materials are present, he says. The water level varies from zero (non-inundated areas) to 3.2 metres, more than the height of the ground floor. Joseph was not personally affected. His house in Ernakulam district is on higher ground; the waters haven’t entered his office in Thrissur district either. But in the immediate vicinity he sees plenty of signs; places and homes marooned; belongings ruined, furniture ripped, sodden electronic goods, cars and vehicles sloshing in water and keeled over, bleached whales of mud and muck, debris and junk, sprawled in homes in most of the ground and first floors of houses and all over the place. For him, the ground is no longer the ground, it’s a swamp. With 40 per cent more rainfall than the usual and more than a million people displaced, the death toll may have been much higher than the official 400 but for the helping hand of neighbours. Particularly notable are the fishermen who toiled day and night to rescue people trapped in their houses. Others provided food and shelter to supplement the state government, army and National Disaster Relief Force’s efforts. Joseph’s understanding is that moisture from the Arabian Sea fuelled the deluge. A massive bank of rain-bearing clouds headed for the Western Ghats, perched on the upper reaches, stalled, condensed and the result was a biblical downpour. He wants, in the near future, maybe in collaboration with the Earth Institute at Columbia University, to find out if this flood is part of the global and regional climate shifts, especially coming after the very severe cyclone Ockhi in 2017. He feels two local factors drove up the magnitude of the flood. He and his team observed nearly 100 landslides in the upper reaches of the Ghats. Open blasting while quarrying sent tremors through charnockite rock, shaking the parent material, and compromising its integrity. When the rain came, the mass became increasingly unstable until it finally slipped down the slopes into river- and stream beds, swelling them further. The second, he says, is the wholesale destruction of wetlands. Up to 15 per cent of Kerala originally comprised wetlands. They’re being destroyed on a massive scale. Had they been standing, they would have absorbed some of the excess water which would eventually have flowed out to the sea. Even paddy fields usually acted as lakes to trap water, which then would flow out to sea. But in this case, Joseph says, that didn’t happen because the fields were construction sites in the state’s mass conversion to other land uses. These two human activities exacerbated the floods. Now, we have to worry about water-borne diseases and sanitation, he says, on the phone, in the midst of sniffles and bouts of coughing. He’s got a viral fevervisiting all those places for the ground survey. They also have to contend with mould spawning on everything moist, making respiratory problems worse. They have to look out for snakes that might have been floating around and sneaked in. For the most part, they have to grapple with themselves first. A flood is not necessarily over even after the waters recede. They leave marks, sweep away a lifetime’s labour in creating a home, they leave persistent memoriesevery new downpour brings an intimation of deluge. India is a sitting duck for extreme events. Flood disasters have become persistent and systemic. In India, millions of people are exposed to floods every year. Vulnerability to floods and economic risk is among the highest in the world. Drawing upon CWC and NDMA sources, the paper, Riverine Flood Hazard: Disaster Risk Reduction in India, which is in press with the Proceedings of the Indian National Science Academy (PINSA), says that the total number of flood deaths between 1953 and 2011 was 97,551, and the economic cost Rs.4.506×1012 at 2017 prices. Research suggests that with rising global temperatures, there will be a significant increase in the frequency and magnitude of extreme rainfall events during the monsoon. Recent extreme events, including Kerala’s, are testimony to the climate disruption already locked in. According to Aqueduct Global Flood Analyzer (AGFA 2017, as referenced by the paper) from the World Resources Institute, a web-based interactive platform which measures river flood impacts by urban damage, affected GDP, and affected population at the country, state, and river basin scale across the globe, India stands at number one, with 4.48 million people exposed to river floods, followed by Bangladesh with 3.48 million and China with 3.28 million. The cost of GDP from flood risk is $14.3 billion, followed by Bangladesh at $5.4 billion. India’s loss of GDP is 15 per cent of the global total. According to Central Water Commission (CWC) data for 2010, 18.3 million people were affected by floods. (AGFA takes into account only urban populations while the CWC’s higher figure has both rural and urban populations.) India is thus a sitting duck for extreme events. Flood disasters have become persistent and systemic in India. On a larger scale, for Kerala’s floods, there is an analogy of sorts with the catastrophic flooding in Texas, US, last year, from hurricane Harvey. Although each case differs and depends on the storm involved, the Kerala flood has parallels with recent extreme events, including Japan between June 28 and July 9, in which 225 people died and about two million people had to be evacuated. In their May 2018 paper titled Hurricane Harvey Links to Ocean Heat Content and Climate Change Adaptation published in Earth’s Future, Kevin Trenberth, a Distinguished Senior Scientist in the Climate Analysis Section at the National Center for Atmospheric Research (NCAR), Boulder, U.S., and his colleagues show for the first time that the heat loss by the ocean caused by the storm (evaporation) matched the latent heat in the rainfall. The high ocean heat content (highest on record for calendar year 2017) feeds the high sea surface temperatures (SSTs) that set the stage for large evaporation, atmospheric moisture, and heavy rains, he explains in an email. In their work, Trenberth continues, they were able to determine how much moisture evaporated from the ocean by measuring ocean heat loss, and were then able to match that with the heat generated by rainfall. So we were able to estimate the evaporated moisture and it matched the independent measurement of rainfall. If the ocean had not been so warm, it would not have evaporated as much and the rain would have been less. Part of the ocean heat was from human effects from global warming, he says. Although there is no study as yet linking the Kerala floods to high ocean heat content, it’s a fair guess that torrential downpours fed off the heat content of the Indian Ocean. Floods depend on the behaviour of rivers. Vishwas Shripad Kale, a retired professor from the University of Pune, says the characteristics of Himalayan and peninsular India’s rivers are very different. In the case of hurricane Harvey, it was also said that the storm took some of the rain it dumped and hurled it back again. Some of the land became so wet that it acted like a water surface and enabled evaporation to occur over what is normally land, Trenberth says. In the case of the Kerala floods too, this could have occurred. Floods also depend on the characteristics and behaviour of rivers. Vishwas Shripad Kale, a retired professor from the University of Pune, who has done extensive work on river behaviour, flows, flood geomorphology and landscape evolution, says the topographic and climatic characteristics of Himalayan and peninsular India’s rivers are very different. In the Himalayas, runoff collects quickly. This happens, to some extent, in the Western Ghats as well. But the main peninsular riversthe Godavari, Krishna, Kaveriflow over a plateau, while rivers in the Himalayas have less space to spread out on the plains. As Kale observes, over the Ganga plains (UP and Bihar) and the Punjab plains flood water from Himalayan rivers spreads and lingers longer due to the gentle slope of the riverine plains. In the peninsula, this happens to some extent over the Deccan plateau (Maharashtra and Mysore plateaux), because of gentler valley slopes in comparison with the Western Ghats. In the monsoon season, cyclones travel across central India, and along their path it rains heavily, triggering floods. Rivers outside their path won’t have large floods. While rivers like the Ganga change course, peninsular river channels are cut into rock, and are relatively stable. They don’t change course much. In old maps of the Ganga plain, Kale says, you find rivers changed course, shifted or moved out of their beds. These changes are not as pronounced in the peninsular rivers. Kale speaks of the Kosi shifting almost 100km in 250 years or so until it was contained by embankments in the 1950s. It was thus both unstable and unpredictable. Many rivers in the Ganga plain keep shifting their courses. The behaviour of rivers is also affected by the spatial and temporal variability of monsoon rains, Kale explains. Spatial variability is simply the regional difference in monsoon rainfall and floods. For example, the tributaries of the Ganga that originate in the Himalayas carry more water and sediment than tributaries originating in Madhya Pradesh, like the Son and Chambal. The latter originate in relatively lower relief and also there is less rain in MP. They are also tributaries of the Ganga but there is a remarkable difference in behaviour. In some rivers, the dischargethe amount of water that flows through the riveris very high because they originate in the high rainfall zone (for example, the Western Ghats). In comparison, the Manjra, a big tributary of the Godavari, which originates in the dry Balaghat range of hills near Ahmednagar district of Maharashtra, carries less water than others. If the rivers have large catchment areas, they collect more rainwater, which means bigger floods. The Godavari has on average greater discharge and its floods are more severe than the Kaveri because the latter has a smaller catchment area. Temporal variability is the behaviour of a river changing with time, from year-to-year variations in monsoon rainfall and intensity over the catchment. It’s not uniform for all rivers. Some rivers may get flooded and others remain unaffected. A huge flood on the Krishna does not necessarily mean the same on the Narmada or Tapi. Cyclones are also important. In the monsoon season, cyclones travel across central India, and along their path it rains heavily, triggering floods. Rivers outside their path won’t have large floods. Size , shape, what’s the relief of the basin, land-use of the basin, forest area, how much water it can retain, where it has wetlandsall these determine floods on the rivers. Therefore, he continues, there is both spatial variability from one region to the other, and temporal variability, related to time. The behaviour of rivers depends on catchment characteristics, the size and shape of it, Kale adds. In the case of the Narmada, it is long, doesn’t have major tributaries so floods mostly happen when it rains at the source. The Narmada’s big floods are caused only by heavy rain in the source area. In the case of the Godavari, which originates in the Western Ghats, (its tributary Wainganga coming from central India, another, Indravati, from the Eastern Ghats), wherever it rains, it collects water. Even when it’s not raining in the Western Ghats but raining in central India or the Eastern Ghats, it will have floods in the lower reaches. If basin slopes are gentle, water flows slowly, takes longer to move. In the mountains, it flows fast and run off collects fast. You have flash floods on coastal rivers in the Konkan and Kerala. Size , shape, what’s the relief of the basin, land-use of the basin, forest area, how much water it can retain, where it has wetlandsall these determine floods on the rivers, he says. Kale also talks about the power of a flood, known as competence. Basically it means how much power it has, to push things, erode things, man-made or natural, to wash away soil, trees and bridges. If the river passes through flat regions with gentle slopes and has a wide channel, it will have low competence. For example, when the Kaveri is flowing over the Mysore plateau, it flows gently, but when it enters a gorge, as downstream of Shivasamudram, it becomes very different. Water is squeezed into a narrow space, velocity increases, and competence increases. It becomes destructive. It’s like squeezing a water hose. It’s the same with a river, behaviour changes, Kale says. Kerala is the most educated, most urbanised and wealthy part of India. That means large-scale deforestation, mining, destruction of riverbeds. Floods serve a useful purpose. They deposit new silt over floodplain areas, increasing soil fertility. In time, river channels silt up but floods clean them of the debris. Floods also help recharge groundwater. Nature has designed everything in such a way that it is in some way or other beneficial to the entire ecosystem, he says. The Kerala floods led Kale to consult the Review of Floods in India during the past 75 years by C. Ramaswamy, published in 1985 by the Indian National Science Academy. The book states that there were severe floods in Kerala, due to more than 127 mm rainfall from July 12-25, 1924. There are reports that in 1961 heavy rain occurred in the upper reaches of the Kaveri. This is 2018, and the Kerala flood is a bit earlier than 100 years from the July 1924 flood, he says…