Your assessed value can increase or decrease each year depending on current market conditions, regardless of whether or not you've made any changes or improvements to your property. Generally, if the market value drops values within the city, your property value will fall to match market value. If values are increasing you will see an increase in your value.
It's important to know that assessors don’t set tax rates, and the revaluation does not change the amount of tax collected by the city, county, school district or technical college. Your property taxes are based on the mill rate, which is the amount of tax payable per $1,000 of property value. If your property assessment increases, it doesn't automatically mean that your property taxes will increase because your assessment is relative to the other properties in the City.