Lake Tahoe will drop below its natural rim by early next week, showing the most severe signs of drought in 10 years. Windy and dry conditions spurred an evaporation rate of almost 1.2 billion gallons per day over the last three days, about 900 times the amount of water the lake loses to Truckee River flows, according to the Federal Watermaster.The lake will fall below its rim approximately two months earlier than last year, meaning that the Truckee River will have only ground water and flows from its tributaries to keep it from going completely dry. Donner Lake is also showing signs of the water squeeze, as the Truckee Carson Irrigation District and the Truckee Meadows Water Authority pulled their water earlier and faster from the lake. Water levels will fall more than a foot every four days until the middle of October, when the lake will be down to minimum flows again.”Our Donner Lake water is a hedge against drought and this is the first year of the last five that we have had to use it,” said Bill Hauck, senior water supply coordinator for the Truckee Meadows Water Authority. “We’re in the fifth year of a drought and each year of the last three the river has dropped off earlier.”Lake Tahoe, which is just less than an inch above the rim, will be down to the rim by Sunday or Monday, depending on evaporation rates, according to the federal watermaster’s office. The lake will stay below that level until enough precipitation falls to raise it again, usually in mid-November.