The sandy ground on the valley floor dries up quickly after winter and warms faster in the summer than the surrounding hills of moist-retaining boulder clay. These conditions affect crops and plants that often bloom 1–2 weeks earlier in the valley than on the northern and southern hillsides. Because of the northern latitude, the number of daylight hours varies considerably between summer and winter. On the summer solstice, the sun rises at 04:26 and sets at 21:58, providing 17 hours 32 minutes of daylight. On the winter solstice, it rises at 08:37 and sets at 15:39 with 7 hours and 2 minutes of daylight. The difference in length of days and nights between summer and winter solstices is 10 hours and 30 minutes. Politics and administration Aarhus is the seat of Aarhus Municipality, and Aarhus City Council (Aarhus Byråd) is also the municipal government with headquarters in Aarhus City Hall. The Mayor of Aarhus since 2010 is Jacob Bundsgaard of the Social Democrats. Municipal elections are held every fourth year on the third Tuesday of November with the next election in 2021. The city council consists of 31 members elected for four-year terms. When an election has determined the composition of the council, it elects a mayor, two deputy mayors and five aldermen from their ranks. Anyone who is eligible to vote and who resides within the municipality can run for a seat on the city council provided they can secure endorsements and signatures from 50 inhabitants of the municipality. The first publicly elected mayor of Aarhus was appointed in 1919. In the 1970 Danish Municipal Reform the current Aarhus municipality was created by merging 20 municipalities. Aarhus was the seat of Aarhus County until the 2007 Danish municipal reform, which substituted the Danish counties with five regions and replaced Aarhus County with Central Denmark Region (Region Midtjylland), seated in Viborg. Subdivisions Aarhus Municipality has 45 electoral wards and polling stations in four electoral districts for the Folketing (national Parliament). The diocese of Aarhus has four deaneries composed of 60 parishes within Aarhus municipality. Aarhus municipality contains 21 postal districts and some parts of another 9. The urban area of Aarhus and the immediate suburbs are divided into the districts Aarhus C, Aarhus N, Aarhus V, Viby J, Højbjerg and Brabrand. Environmental planning Aarhus has increasingly been investing in environmental planning and, in accordance with national policy, aims to be