There are many papers about Haar wavelets applications. For example, method for solving ODEs with Haar wavelets described by Ü. Lepik (2009) Haar wavelet method for solving stiff differential equations, Mathematical Modelling and Analysis, 14:4, 467-481. To link to this article: http://dx.doi.org/10.3846/1392-6292.2009.14.467-481
Method for solving integral equations proposed by Ülo Lepik and Enn Tamme, Solution of nonlinear Fredholm integral equations via the Haar wavelet method, Proc. Estonian Acad. Sci. Phys. Math., 2007, 56, 1, 17–27.