of Central Java and East Java, which eventually empties in Gresik. Brantas River and Bengawan Solo are managed by Perum Jasa Tirta I. On the slopes of Mount Lawu near the border with Central Java are Sarangan, a natural lake. The main dam in East Java, among others Ir. Sutami and Selorejo Dam, which is used for irrigation, fish farming and tourism. Climate East Java has a tropical monsoon and savanna climate at lower elevation and subtropical at higher elevation. Compared with the western part of Java Island, East Java in general has less rainfall. Average rainfall is 1,900 mm per year, with a rainy season during the 100 days. The average temperature ranges between 19-34 °C. Temperatures in the lower mountain areas, and even in areas Ranu Pani (slopes of Mount Semeru), temperatures can reach –4 °C, causing a frost and fall of light snow. Administrative divisions East Java is divided into 29 kabupaten (or regencies), and 9 kotamadya (or cities). This division has remained unchanged since the creation of the province, except for the creation of the new city of Batu on 21 June 2001 (by separation from Malang Regency). These regencies and cities with their areas and populations at the 2000, 2010 and 2020 Censuses, together with the official estimates as at mid 2021, are listed below, grouped geographically into five (unofficial) sub-regions entirely for convenience of access. The sub-regions have no official status. These regencies and cities are divided at 2021 into 666 districts (kecamatan) which are in turn composed of 8,501 administrative villages (rural desa and urban kelurahan): Note: (a) the 2000 population of Batu City is included in the total for Malang Regency, from which it was separated on 21 June 2001. Demography According to the 2000 census, East Java had 34,765,993 people, which increased to 37,476,757 people at the 2010 Census, and to 40,665,595 at the 2020 Census, making it the second most populous Indonesian province after West Java. The official estimate as at mid 2021 was 40,878,789. Akin to Central Java, the region's birth rates are not necessarily any lower than the rest of Java, however due to net population outflows, especially in times of calamity, not limited to volcanic eruptions or droughts, the region has varying rates of population growth that are generally lower than national average. Ethnic Javanese dominate the Java mainland as well as the total population of the