Geography of Kerala

Kerala is prone to several natural hazards, the most common of them being landslides, flooding, lightning, drought, coastal erosion, earthquakes, Tsunami, wind fall and epidemics [Yashodharan et al., (2007)] .

Landslides

The highlands of Kerala experience several types of landslides, of which debris flows are the most common. They are called ‘Urul Pottal’ in the local vernacular. The characteristic pattern of this phenomenon is the swift and sudden downslope movement of highly water saturated overburden containing a varied assemblage of debris material ranging in size from soil particles to boulders, destroying and carrying with it every thing that is lying in its path. The west facing Western Ghats scarps that runs the entire extent of the mountain system is the most prone physiographic unit for landslides. The highlands of the region experience an annual average rainfall as high as 500 cm from the South-West, North-East and Pre-Monsoon showers. A survey of ancient documents and early news papers indicates a lesser rate of slope instability in the past. The processes leading to landslides were accelerated by anthropogenic disturbances such as deforestation since the early 18th century, terracing and obstruction of ephemeral streams and cultivation of crops lacking capability to add root cohesion in steep slopes. The events have become more destructive given the increasing vulnerability of population and property. Majority of mass movements have occurred in hill slopes >20^o along the Western Ghats scarps, the only exception being the coastal cliffs. Studies conducted in the state indicates that prolonged and intense rainfall or more particularly a combination of the two and the resultant pore pressure variations are the most important trigger of landslides. The initiation zone of most of the landslides was typical hollows generally having degraded natural vegetation. A survey of post landslide investigation and news paper reports enabled the identification of 29 major landslide events in the state. All except 1 of the 14 districts in the state are prone to landslides. Wayanad and Kozhikode districts are prone to deep seated landslides while Idukki and Kottayam are prone to shallow landslides [Kuraikose et al., 2008] .

Flooding

Although the Kerala State does not experience floods as severe as in the Indo-Gangetic plains, incidence of floods in the State is becoming more frequent and severe. Continuous occurrence of high intensity rainfall for a few days is the primary factor contributing to the extreme floods in the State. Other factors include wrong landuse practices and mismanagement of the water resources and forests. The human interventions contributing to flood problems are predominantly in the form of reclamation of wetlands and water bodies, change in landuse pattern, construction of dense networks of roads, establishment of more and more settlements, deforestation in the upper catchments etc. Increasing floodplain occupancy results in increasing flood damages. Urban floods result from blocked or inadequate storm sewers and due to increased urbanization. A number of extreme flood events occurred during the last century causing considerable damage to life and property highlight the necessity for proper flood management measures in the State. The flood problems are likely to worsen with the continued floodplain occupancy and reclamation of water bodies and wetlands. It is estimated that about 25% of the total geographical area accommodating about 18% of the total population of the State is prone to floods ^[3] .

Lightning

Kerala is a place of high lightning incidence compared to most of the other parts in India. Weather and location of Western Ghats together cause formation more lightning clouds resulting in higher incidence. This is the main driving force of this natural hazard. Relatively higher population density and vegetation density result in more casualties. Lack of awareness also aggravates the situation. Accidents caused by ground conduction from trees, which is a special feature of Kerala, add to the casualties and loss of property. When more number of clouds are formed, greater exposure by larger population and vegetation density constitute the main the pressures on the state. Less preparedness and the special feature of ground conduction adds to the pressure. The present state of affairs show that in a year the months April, May, October and November have relatively much higher lightning incidence. Similarly the most active time of the day is between 1500 hrs. and 1900 hrs. Of the fourteen districts five have much more incidence than others. The relatively severe impact of the hazard on the state and its people is seen from the very high casualty rates of 71 deaths, 112 injuries and 188 accidents per annum. Loss to telephone sector also is very high. In addition to the above networked systems and electrical equipment also get destroyed ^[3] .

Drought

Kerala has been experiencing increasing incidents of drought in the recent past due to the weather anomalies and developmental pressures resulting from the changes in land use, traditional practices, and life style of the people. The increase in population and subsequent expansion in irrigated agriculture, and industrial growth necessitated the exploitation of more water resources. The changes in the land and water management practices affected the fresh water availability during summer months. Although the deviation in the annual rainfall received in Kerala, in any year from the long term average is very small, there is considerable variation in the rainfall availability during the different seasons. About 95 percent of annual rainfall is confined to a six-month monsoon period between June and November, leaving the remaining six months as practically dry. Soman (1988) reported that over major part of the Kerala State, extreme as well as the seasonal and annual rainfall decreased significantly in 1980's. The maximum decrease in rainfall occurred in the highland regions where the rainfall is more compared to other areas. The changes in rainfall pattern may have association with the environmental modifications due to human interventions on the natural ecosystems. The State of Kerala experiences seasonal drought conditions every year during the summer months. Even in the years of normal rainfall, summer water scarcity problems are severe in the midland and highland regions. Severe drought conditions often result from the anomalies in monsoon rainfall combined with the various anthropogenic pressures. A study on the incidence of droughts based on the aridity index shows that during the period 1871- 2000, the State of Kerala experienced 66 drought years, out of which, twelve each were moderate and severe droughts. The droughts have a large dimension of economic, environmental and social impacts. With the implementation of a number of irrigation projects, the idea of drought in Kerala slowly shifted to unirrigated paddy, and upland crops. The water scarcity in summer is mainly reflected in dry rivers and lowering of water table. This adversely affects the rural and urban drinking water supply. As seen in the majority of drought incidents, even a 20% fall in the northeast monsoon, can make the water scarcity situation worse during the summer. Since the State has more of perennial plantation crops compared to other places of India, the effect of a drought year in Kerala continues to be felt for several more years after it has occurred. Thus, for better planning of the drought management measures, the term drought with reference to plantation crops should be redefined based on rainfall received or available soil moisture during summer months instead of total monsoon rainfall ^[3] .

Tsunami

The Kerala coast located in the shadow zone with respect to the direction of propagation of the tsunami, encountered unexpected devastation. Although tsunami affected parts of Kerala coast, maximum devastation was reported in the low coastal land of Kollam, Alleppey and Ernakulam districts, particularly a strip of 10 km in Azhikkal, Kollam district. This varying effect along the coast could be attributed to local amplification of tsunami waves in certain regions. About 176 people were killed and 1600 injured in the coastal belt. Further, the tsunami pounded 187 villages affecting nearly 25 lakh persons in Kerala. As many as 6280 dwelling units were completely destroyed, 11175 were partially damaged and nearly 84773 persons were evacuated from the coastal areas and accommodated in 142 relief camps after tsunami. As this tsunami is believed to be first of its kind to have significantly affected the Kerala coast, the post-tsunami field investigations and measurements would give valuable information on various changes brought by the tsunami. Immediately after the tsunami, several organizations have carried out field surveys in many affected areas along the coast ^[3] .

References

1. Harvard reference
Surname1 = Jose
Given1 = AI (editor) "et al"
Year = 2002
Title = Package of Practices Recommendations: Crops
Publisher = Kerala Agricultural University
URL = http://www.kau.edu/pop/map_of_agro_zones.htm
Access-date = January 18, 2006.

2. Harvard reference
Surname1 = Chacko
First1 = T
Surname2 = Renuka
First2 = G
Year = 2002
Title = Temperature mapping, thermal diffusivity and subsoil heat flux at Kariavattom of Kerala
Journal = Proc Indian Acad Sci (Earth Planet Sci)
URL = http://www.ias.ac.in/epsci/mar2002/Esb1439.pdf
Access-date = January 12, 2006.

3. Harvard reference
Surname1 = Yesodharan
First1 = E.P
Surname2 = Kokkal
First2 = K
Surname3 = Harinarayanan "(Editors)"
First3 = P
Year = 2007
Title = State of Environment Report of Kerala 2007 - Volume II: Natural Hazards
Journal = Kerala State Council for Science, Technology and Environment, Government of Kerala, Thiruvananthapuram, India
URL = http://kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_firstpages.htm
Access-date = July 01, 2008.

4. Harvard reference
Surname1 = Kuriakose
Given1 = S.L
Surname2 = Sankar
Given2 = G
Surname3 = Muraleedharan
Given3 = C
Year = 2008
Title = History of landslide susceptibility and a chorology of landslide prone areas in the Western Ghats of Kerala, India
Journal = Environmental Geology "(DOI: 10.1007/s00254-008-1431-9)"
URL = http://www.springerlink.com/content/c1q6465428351032/
Access-date = July 01, 2008.