Udawalawe lies on the boundary of Sri Lanka's wet and dry zones. Plains dominate the topography, though there are also some mountainous areas. The Kalthota Range and Diyawini Falls are in the north of the park and the outcrops of Bambaragala and Reminikotha lie within it. The park has an annual rainfall of, most of which falls during the months of October to January and March to May. The average annual temperature is about, while relative humidity varies from 70% to 83%. Well-drained reddish-brown soil is the predominant soil type, with poorly drained low humic grey soils found in the valley bottoms. Mainly alluvial soils form the beds of water courses
Ecology
The habitat surrounding at the reservoir includes marshes, the Walawe river and its tributaries, forests and grasslands. Dead trees standing in the reservoir are visual reminders of the extent of forest cover before the construction of the Udawalawe Dam. Green algae, including Pediastrum and Scenedesmus spp., and blue green algae species such as Microsystis, occur in the reservoir. Areas of open grassland are abundant as a result of former chena farming practices. There is a plantation of teak beyond the southern boundary, below the dam, which was planted before the declaration of the park. Species recorded from the park include 94 plants, 21 fish, 12 amphibians, 33 reptiles, 184 birds, and 43 mammals. Additionally 135 species of butterflies are among the invertebrates found in Udawalawe.
Flora
Hopea cordifolia, Memecylon petiolatum, Erythroxylon zeylanicum, and Jasminum angustifolium are endemic floral species recorded from the park. Hopea cordifolia is found along the river along with Terminalia arjuna. Panicum maximum and Imperata cylindrica are important food sources for the elephants. Chloroxylon swietenia, Berrya cordifolia, Diospyros ebenum, Adina cordifolia, Vitex pinnata, Schleichera oleosa, and Diospyros ovalifolia are the common taller trees. Terminalia bellirica and Phyllanthus emblica are plants of medicinal value found in the forest. Cymbopogon confertiflorus grass species and Grewia tiliifolia bushes are common in the grasslands.
s, painted-lip lizards, mugger crocodiles, Asian water monitors, Bengal monitors and 30 species of snake are found in the park. Garra ceylonensis is an endemic fish species recorded in park. Introduced Oreochromis spp., giant gourami, catla, and rohu are important food fish species found in the reservoir.
Conservation
Clearing natural forests and planting monospecies cultures such as pine and eucalyptus are causing reduced water levels in the Walawe river. Encroachment by human settlements, poaching, illegal logging, gem mining, overgrazing and chena farming are major threats to the park. Lantana camara and Phyllanthus polyphyllus are invasive weeds affecting the food plants of the elephants. Occasions of elephants being shot with illegal muzzleloader guns has been reported.
Tourism
In the six months ending in August 2009, the park earned revenue of Rs. 18.2 million. From 1994 to 2001 some 423,000 people visited the park, 20% of them foreigners. For the 1998-2001 period average annual revenue was 280,000. Postage stamps bearing the images of four wild animals of Udawalawe were issued on 31 October 2007 in the series "National Parks of Sri Lanka", featuring water buffalo, Sri Lankan elephant, ruddy mongoose and tufted grey langur.