Here are the official Kansas state revenue statistics:
To find out whether revenues have been falling and if so from what source just compare an entry for 2015 with that of 2014. For example, the cumulative income tax revenue in March 2014 for fiscal year 2014 was $1.91 billion (total tax revenue was $4.13 billion) and for March 2015 was $1.84 billion (total was $4.08). Then you would have to investigate whether or not the decline was caused by a declining income base (because of the recession) or declining income tax rates (because of Brownback’s policy). Then you would need to look at the expenditure side of the budget to see if rising expenditures are pushing up the deficit as well as falling tax revenues.