1979, and 2.3% between 1990 and 1991. With deforestation and cultivation increasing, a permeable mixture of gravel, boulders and sand evolves, which leads to a sinking water table. But where layers consist of clay and fine sediments, the groundwater rises to the surface and heavy sediment is washed out, thus enabling frequent and massive floods during monsoon, such as the 2008 Bihar flood. Geography In India, the Terai extends over the states of Haryana, Uttarakhand, Uttar Pradesh, Bihar and West Bengal. These are mostly the districts of these states that are on the India–Nepal border: Haryana: Panchkula district Uttarakhand: Haridwar district, Udam Singh Nagar and Nainital districts Uttar Pradesh: Pilibhit district, Lakhimpur Kheri district, Bahraich district, Shravasti district, Balrampur district, Gorakhpur district, Siddharthnagar district and Maharajganj district Bihar: West Champaran district, East Champaran district, Sitamarhi district, Madhubani district, Supaul district, Araria district, Kishanganj district West Bengal: Siliguri subdivision of Darjeeling district, Jalpaiguri Sadar subdivision of Jalpaiguri district Inner Terai The Inner Terai Valleys of Nepal consists of five elongated valleys located between the lower Himalayan Range and Sivalik Hills. From north-west to south-east these valleys are: Surkhet Valley in the Surkhet district, north of the Kailali and Bardiya districts; Dang Valley in the Dang Deokhuri district; Deukhuri Valley located south of the Dang Valley; Chitwan Valley stretching across the Chitwan and Makwanpur districts; Kamala Valley, also called Udayapur Valley, in the Udayapur district north of the Siraha and Saptari districts. Outer Terai The Outer Terai begins south of the Sivalik Hills and extends to the Indo-Gangetic Plain. In the Far-Western Region, Nepal it comprises the Kanchanpur and Kailali districts, and in the Mid-Western Region, Nepal Bardiya and Banke districts. Farther east, the Outer Terai comprises the Kapilvastu, Rupandehi, Nawalparasi, Parsa, Bara, Rautahat, Sarlahi, Mahottari, Dhanusa, Siraha, Saptari, Sunsari, Morang and Jhapa districts. Protected areas Several protected areas were established in the Terai since the late 1950s: Sonaripur Wildlife Sanctuary, now Dudhwa National Park in 1958 Kishanpur Wildlife Sanctuary in 1972 Chitwan National Park in 1973 Katarniaghat Wildlife Sanctuary in 1975 Shuklaphanta Wildlife Reserve in 1976 Koshi Tappu Wildlife Reserve in 1976 Udaypur Wildlife Sanctuary in 1978 Rajaji National Park in 1983 Parsa National Park in 1984 Bardia National Park in 1988 Valmiki National Park in 1989 Jhilmil Jheel Conservation Reserve in 2005 Banke National Park in 2010 Sohagi Barwa Wildlife Sanctuary of Maharajganj district Climate Based on the Köppen–Geiger climate